fix: preserve MySQL schema fidelity

README.md

@@ -79,6 +79,25 @@ block contents. Raw SQL expressions remain executable input. See the
 [PostgreSQL writer documentation](pkg/writers/pgsql/README.md#identifier-and-value-handling)
 for library options and details.
 
+#### MySQL fidelity and strict conversion
+
+MySQL output now preserves foreign keys and their actions, checks, indexes,
+unsigned types, dimensions, generated columns, and native defaults. Known
+unsupported features produce warnings. Add `--strict-conversion` to reject
+lossy MySQL output before writing a file or executing DDL:
+
+```bash
+relspec convert --from mysql --from-conn "$MYSQL_DSN" \
+                --to mysql --to-path schema.sql --strict-conversion
+```
+
+Schema jobs can set `options.strict_conversion: true`. This check currently
+covers MySQL output; it does not guarantee lossless conversion to every format.
+The live suite covers MySQL 8.4 / InnoDB, including JSON/YAML intermediates.
+See the [MySQL capability matrix](docs/MYSQL_FIDELITY.md) for unsupported objects,
+metadata, SQL-mode requirements, and execution limits. Output creates tables in
+existing databases; it is not a data copy or a rerunnable migration.
+
 ### `batch` — Convert many inputs in one run
 
 Converts each input independently (one output per input, unlike `--from-list`
@@ -202,7 +221,9 @@ references, which are expanded and safety-checked during pre-flight. See
 
 Use `options.lowercase_identifiers: true` per job, or
 `relspec job run build-schema --lowercase` to enable lowercasing for schema outputs
-throughout the selected job plan.
+throughout the selected job plan. For MySQL schema output,
+`options.strict_conversion: true` or `--strict-conversion` rejects known lossy
+conversions before writing.
 
 ### `scripts` — SQL scripts and embedded assets
 

cmd/relspec/convert.go

@@ -181,12 +181,12 @@ Examples:
 }
 
 func init() {
-	convertCmd.Flags().StringVar(&convertSourceType, "from", "", "Source format (dbml, dctx, drawdb, graphql, json, yaml, gorm, bun, drizzle, prisma, typeorm, pgsql, sqlite)")
+	convertCmd.Flags().StringVar(&convertSourceType, "from", "", "Source format (dbml, dctx, drawdb, graphql, json, yaml, gorm, bun, drizzle, prisma, typeorm, pgsql, mssql, mysql, sqlite)")
 	convertCmd.Flags().StringVar(&convertSourcePath, "from-path", "", "Source file path (for file-based formats)")
-	convertCmd.Flags().StringVar(&convertSourceConn, "from-conn", "", "Source connection string (for pgsql) or file path (for sqlite)")
+	convertCmd.Flags().StringVar(&convertSourceConn, "from-conn", "", "Source connection string (pgsql, mssql, mysql) or file path (sqlite)")
 	convertCmd.Flags().StringSliceVar(&convertFromList, "from-list", nil, "Comma-separated list of source file paths to read and merge (mutually exclusive with --from-path)")
 
-	convertCmd.Flags().StringVar(&convertTargetType, "to", "", "Target format (dbml, dctx, drawdb, graphql, json, yaml, gorm, bun, drizzle, prisma, typeorm, pgsql)")
+	convertCmd.Flags().StringVar(&convertTargetType, "to", "", "Target format (dbml, dctx, drawdb, graphql, json, yaml, gorm, bun, drizzle, prisma, typeorm, pgsql, mssql, mysql, sqlite)")
 	convertCmd.Flags().StringVar(&convertTargetPath, "to-path", "", "Target output path (file or directory)")
 	convertCmd.Flags().StringVar(&convertPackageName, "package", "", "Package name (for code generation formats like gorm/bun)")
 	convertCmd.Flags().StringVar(&convertSchemaFilter, "schema", "", "Filter to a specific schema by name (required for formats like dctx that only support single schemas)")
@@ -449,7 +449,7 @@ func readDatabaseForConvert(dbType, filePath, connString string) (*models.Databa
 	return db, nil
 }
 
-func writeDatabase(db *models.Database, dbType, outputPath, packageName, schemaFilter string, flattenSchema bool, nullableTypes, nullableArrays string, continueOnError bool, extraFields string) error {
+func writeDatabase(db *models.Database, dbType, outputPath, packageName, schemaFilter string, flattenSchema bool, nullableTypes, nullableArrays string, continueOnError bool, extraFields string, strict ...bool) error {
 	if lowercaseIdentifiers {
 		var err error
 		schemaFilter = strings.ToLower(schemaFilter)
@@ -462,6 +462,9 @@ func writeDatabase(db *models.Database, dbType, outputPath, packageName, schemaF
 	var writer writers.Writer
 
 	writerOpts := newWriterOptions(outputPath, packageName, flattenSchema, nullableTypes, nullableArrays, continueOnError)
+	if len(strict) > 0 {
+		writerOpts.StrictConversion = writerOpts.StrictConversion || strict[0]
+	}
 	if extraFields != "" {
 		extraFieldsJSON, err := loadExtraFields(dbType, extraFields)
 		if err != nil {
@@ -611,6 +614,19 @@ func validateWriteTarget(db *models.Database, dbType, packageName, schemaFilter,
 		"pgsql", "postgres", "postgresql", "sql",
 		"mssql", "sqlserver", "mssql2016", "mssql2017", "mssql2019", "mssql2022",
 		"sqlite", "sqlite3", "prisma", "typeorm", "graphql", "gql":
+	case "mysql", "mariadb":
+		selected := db
+		if schemaFilter != "" {
+			selected = &models.Database{}
+			for _, s := range db.Schemas {
+				if s.Name == schemaFilter {
+					selected.Schemas = append(selected.Schemas, s)
+				}
+			}
+		}
+		if _, err := wmysql.NewWriter(newWriterOptions("", packageName, false, "", "", false)).Statements(selected); err != nil {
+			return err
+		}
 	case "gorm", "bun":
 		if packageName == "" {
 			return fmt.Errorf("package name is required for %s format (use --package flag)", dbType)

cmd/relspec/job.go

@@ -874,7 +874,7 @@ func writeJobOutput(rj *resolvedJob, db *models.Database, lg *jobLogger) error {
 	lg.logf("writing output: %s (%s)", rj.outputPath, format)
 
 	write := func(target string) error {
-		return writeDatabase(db, format, target, o.Package, o.Schema, o.FlattenSchema, o.Types, o.ArrayNullable, o.ContinueOnError, "")
+		return writeDatabase(db, format, target, o.Package, o.Schema, o.FlattenSchema, o.Types, o.ArrayNullable, o.ContinueOnError, "", o.StrictConversion)
 	}
 	// Single-file formats are written to a temp file and renamed into place so
 	// a failure never leaves a partial or truncated output. Directory-emitting

cmd/relspec/prisma_options.go

@@ -32,5 +32,6 @@ func newWriterOptions(outputPath, packageName string, flattenSchema bool, nullab
 		Prisma7:              prisma7,
 		ContinueOnError:      continueOnError,
 		StrictDirectives:     strictDirectives,
+		StrictConversion:     strictConversion,
 	}
 }

cmd/relspec/root.go

@@ -18,6 +18,7 @@ var (
 	noVersion            bool
 	silent               bool
 	strictDirectives     bool
+	strictConversion     bool
 	lowercaseIdentifiers bool
 	typeMapFlags         []string
 	typeMappings         map[string]string
@@ -62,6 +63,7 @@ func init() {
 	rootCmd.PersistentFlags().StringArrayVar(&typeMapFlags, "type-map", nil, "Override a SQL-to-Go type mapping for bun/gorm output as sqltype=gotype (repeatable), e.g. --type-map uuid=uuid.UUID --type-map numeric=decimal.Decimal")
 	rootCmd.PersistentFlags().BoolVar(&noVersion, "no-version", false, "Suppress the RelSpec version header")
 	rootCmd.PersistentFlags().BoolVar(&silent, "silent", false, "Suppress progress and status messages (errors are still shown)")
+	rootCmd.PersistentFlags().BoolVar(&strictConversion, "strict-conversion", false, "Reject known lossy MySQL schema conversions before writing or executing output")
 	rootCmd.PersistentFlags().BoolVar(&strictDirectives, "strict-directives", false, "Fail on unknown or untranslatable DBML dialect directives (@postgres:, @sqlite:, …)")
 }
 

cmd/relspec/strict_conversion_test.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.warky.dev/wdevs/relspecgo/pkg/jobs"
+	"git.warky.dev/wdevs/relspecgo/pkg/models"
+)
+
+func TestStrictConversionOptionAndDryRun(t *testing.T) {
+	prior := strictConversion
+	strictConversion = true
+	t.Cleanup(func() { strictConversion = prior })
+	if flag := rootCmd.PersistentFlags().Lookup("strict-conversion"); flag == nil {
+		t.Fatal("missing --strict-conversion")
+	}
+	db := models.InitDatabase("shop")
+	s := models.InitSchema("shop")
+	table := models.InitTable("users", "shop")
+	col := models.InitColumn("value", "users", "shop")
+	col.Type = "unknown_type"
+	table.Columns[col.Name] = col
+	s.Tables = append(s.Tables, table)
+	db.Schemas = append(db.Schemas, s)
+	if err := validateWriteTarget(db, "mysql", "", "", ""); err == nil || !strings.Contains(err.Error(), "lossy MySQL") {
+		t.Fatalf("dry run bypassed strict validation: %v", err)
+	}
+	strictConversion = false
+	out := filepath.Join(t.TempDir(), "out.sql")
+	rj := &resolvedJob{job: &jobs.Job{Output: &jobs.Output{Format: "mysql"}, Options: jobs.Options{StrictConversion: true}}, outputPath: out}
+	if err := writeJobOutput(rj, db, &jobLogger{file: io.Discard}); err == nil || !strings.Contains(err.Error(), "lossy MySQL") {
+		t.Fatalf("job option bypassed strict validation: %v", err)
+	}
+	if _, err := os.Stat(out); !os.IsNotExist(err) {
+		t.Fatalf("strict job created output: %v", err)
+	}
+}

docs/JOB_FILES.md

@@ -191,6 +191,7 @@ jobs:
                                                # (file output = full DDL); set options.full_ddl to force full DDL
       overwrite: false                         # default false
     options:
+      strict_conversion: false                # reject known lossy MySQL output before writing
       lowercase_identifiers: false             # lowercase names/references; SQL expressions and data keep their case
       flatten_schema: false
       schema: public

docs/MYSQL_FIDELITY.md

@@ -0,0 +1,131 @@
+# MySQL schema fidelity
+
+The MySQL reader/writer preserves the table-schema features below. It generates
+DDL for **new tables in existing databases**, not migrations or data copies.
+MySQL 8.4 / InnoDB is exercised by the live suite. The reader uses MySQL 8.0.23+
+metadata (including functional indexes, checks, spatial metadata, and invisible
+columns); older MySQL versions and the `mariadb` alias are not certified by this
+suite and may return explicit metadata-query errors.
+
+## Conversion diagnostics
+
+MySQL output warns on stderr when it encounters known unsupported features.
+Add `--strict-conversion` to reject these conversions before opening an output
+file or connecting to an output database:
+
+```bash
+relspec convert --from mysql --from-conn "$MYSQL_DSN" \
+  --to mysql --to-path schema.sql --strict-conversion
+
+relspec convert --from json --from-path schema.json \
+  --to mysql --to-path schema.sql --strict-conversion --dry-run
+```
+
+The flag also applies to MySQL output from `batch`, `split`, and schema jobs.
+Jobs can set `options.strict_conversion: true`. Library callers use
+`writers.WriterOptions.StrictConversion`; `Warning func(string)` collects
+non-strict diagnostics instead of printing them. `mysql.Writer.Statements`
+performs the same preflight without opening a destination and returns structured
+SQL statements suitable for execution without splitting on semicolons.
+
+Strict conversion currently covers **MySQL output**. It is not a general
+losslessness check for other writers or a validator of arbitrary SQL fragments.
+Warnings identify the object and omitted or changed feature. Inspect them before
+using non-strict output; unsupported index types are omitted, while a partial
+index's predicate and INCLUDE columns cannot be represented in MySQL.
+
+## MySQL capability matrix
+
+| Feature | Reader → model | Model → MySQL DDL |
+| --- | --- | --- |
+| Ordered columns, nullability, primary/composite keys | Preserved | Preserved |
+| Unique/composite keys | Preserved, including backing indexes | Preserved once; no duplicate unique index |
+| Foreign/composite keys and DELETE/UPDATE actions | Preserved | Added after all tables, allowing forward references/cycles |
+| CHECK and NOT ENFORCED CHECK | Preserved | Preserved |
+| BTREE, FULLTEXT, SPATIAL indexes | Preserved | Emitted; engine restrictions still apply |
+| Expression/prefix/descending/invisible index parts | Preserved in `Index.KeyParts` and metadata | Preserved |
+| HASH indexes | Preserved | Engine-dependent; incompatible engine produces a diagnostic |
+| Integer unsignedness; mediumint; enum/set; binary/blob/text variants | Canonical type plus native declaration | Native declaration preserved |
+| Length, numeric precision/scale, fractional seconds | Typed dimensions plus native declaration | Preserved; canonical dimensions also supported |
+| Defaults, including SQL expressions, bit/binary literals and multiline text | Values plus native SQL spelling from SHOW CREATE | Preserved |
+| Auto-increment and current next value | Preserved | Preserved |
+| Stored/virtual generated columns, ON UPDATE, invisible columns | Preserved | Preserved |
+| Engine, table/column collation, charset and comments | Preserved | Preserved |
+| Views, triggers, routines, events, partitioned tables | Names recorded in `mysql_unsupported` | Diagnostic; bodies/partition definitions are not emitted |
+| Nonempty table CREATE_OPTIONS; native parser/storage/engine attributes; spatial SRID | Recorded as unsupported attributes | Diagnostic; not emitted |
+| Partial/INCLUDE indexes, unsupported index methods | Retained when supplied in the model | Diagnostic |
+| Deferrable constraints, identity semantics, timestamptz, jsonb storage | Retained when supplied in the model | Diagnostic for unsupported/different semantics |
+| Standalone sequences/enums/domains, ownership/permissions, scripts and dialect directives | Retained when supplied in the model | Diagnostic; not emitted |
+| Data, grants, users, server/plugin configuration | Outside the reader's schema contract | Outside the writer's contract |
+
+Diagnostics depend on the objects visible to the connection account. They cover
+known modeled/discovered features, not every engine/plugin extension. The server
+still validates SQL expressions, engine rules, and references at execution time.
+For example, source and target engines must support the constraints requested.
+
+## Preservation across intermediate formats
+
+| Path | Scope |
+| --- | --- |
+| MySQL → model → MySQL | Live-tested for the features above on MySQL 8.4 / InnoDB |
+| MySQL → JSON → model → MySQL | Live-tested; preserves typed index parts and MySQL metadata |
+| MySQL → YAML → model → MySQL | YAML serializes the same fields/metadata; covered by the live round-trip test |
+| Other source/target formats | Their own mappings apply; MySQL-specific metadata and semantics are not certified to survive |
+
+Native declarations and defaults are stored in column metadata as `mysql_type`
+and `mysql_default_sql`. Reader-generated signatures (`mysql_type_signature`,
+`mysql_default_value`) prevent these spellings from silently overriding edited
+types/dimensions/defaults. Editing canonical dimensions invalidates the native
+type signature, produces a diagnostic, and uses the canonical mapping instead.
+For a binary default, the logical default is its SQL hex/literal spelling so it
+survives serialization without invalid UTF-8.
+
+Other metadata includes `mysql_charset`, `mysql_generation_storage`,
+`mysql_default_expression`, `mysql_on_update`, `mysql_invisible`, table
+`mysql_engine` / `mysql_collation` / `mysql_auto_increment`, index
+`mysql_visible`, and check `mysql_enforced`. Unknown `mysql_*` metadata produces
+a diagnostic. For a manually authored expression default, set
+`mysql_default_expression: true`; otherwise strings are literal values.
+`Index.KeyParts` is authoritative when present; `Index.Columns` remains the
+compatibility representation for simple indexes.
+
+Raw native type declarations, default SQL, generation/check/index expressions,
+and ON UPDATE expressions are executable SQL input. Lowercasing changes names
+and structured index parts but leaves expressions untouched; update references
+inside raw SQL yourself when using `--lowercase`.
+
+## Applying the output
+
+Create the destination database/schema first. Qualified names are preserved,
+including foreign-key target schemas. Adjust them explicitly when restoring to
+a different database. Output assumes standard MySQL backslash escaping;
+`NO_BACKSLASH_ESCAPES` or `ANSI_QUOTES` on the source produces a conversion
+diagnostic, and live execution refuses these target modes before DDL. File consumers must use the same
+supported mode. Other SQL-mode incompatibilities surface as server errors.
+
+`CREATE TABLE IF NOT EXISTS` does not reconcile existing definitions. Foreign
+keys use `ALTER TABLE ADD CONSTRAINT` and therefore repeated application can
+fail on existing constraints. This is creation DDL, not a rerunnable migration.
+Live execution stops on the first SQL error by default. Explicit
+`ContinueOnError` attempts later statements and still returns an error if any
+fail. MySQL DDL implicitly commits; `AtomicExecution` is rejected. PostgreSQL's
+shared execution-report support is not yet implemented for this writer.
+
+## Verification
+
+```bash
+./tests/dbtest/dbtest.sh test mysql
+# Or use your own disposable database:
+RELSPEC_TEST_MYSQL_CONN="$MYSQL_DSN" go test -mod=vendor ./pkg/readers/mysql ./pkg/writers/mysql
+```
+
+The live tests compare MySQL's `SHOW CREATE TABLE` definitions, normalizing only
+temporary target-name suffixes and nonsemantic ordinary-index display order.
+They re-read the target, exercise constraint enforcement/default values, and
+verify unsupported objects produce warnings or strict failures without touching
+an existing output file. Test fixtures are removed after each run.
+
+Metadata references: [COLUMNS](https://dev.mysql.com/doc/refman/8.4/en/information-schema-columns-table.html),
+[STATISTICS](https://dev.mysql.com/doc/refman/8.4/en/information-schema-statistics-table.html),
+[TABLE_CONSTRAINTS](https://dev.mysql.com/doc/refman/8.4/en/information-schema-table-constraints-table.html),
+and [REFERENTIAL_CONSTRAINTS](https://dev.mysql.com/doc/refman/8.4/en/information-schema-referential-constraints-table.html).

docs/audit_1.md

@@ -20,6 +20,11 @@ Implementation batches (2026-10-12):
 - [x] **Requested lowercase option:** `--lowercase` on convert/batch/merge/split/templ/job run, job `options.lowercase_identifiers`, and PostgreSQL `WriterOptions.LowercaseIdentifiers` normalize names and structured references on a copy, rejecting collisions. SQL expressions, defaults, comments, enum values, and data keep their case; callers must adjust references inside raw SQL themselves.
 - [x] **A08, SQL-aware substitution/execution:** embeds use one-pass literal substitution, preserving dollar characters and preventing replacement rescanning. Named parameters and embed directives respect SQL strings, quoted identifiers, nested comments, casts, and dollar bodies; duplicate/unused embed variables fail. MySQL executes structured generated statements without splitting multiline literals or stripping their contents.
 
+- [x] **A06, nullable MySQL catalogs:** constraint references, functional-index columns/expressions, index prefix/direction fields, column dimensions/collations/generation metadata, and optional table auto-increment counters use nullable destinations. Queries qualify joined columns. Live primary/unique/composite/functional-key reads pass, including unsigned auto-increment values beyond signed 64-bit range.
+- [x] **A07, scoped MySQL fidelity and diagnostics:** native types/default spellings and typed dimensions/index parts survive MySQL → model → JSON/YAML → DDL. Output emits foreign keys/actions after all tables, checks/enforcement, unique/ordinary/functional/prefix/descending/invisible/fulltext indexes, generated columns, comments/collations/charsets, ON UPDATE, invisible columns, and auto-increment counters. Known unsupported objects/attributes produce warnings or `--strict-conversion` / job `options.strict_conversion` / library `StrictConversion` failures before output or connection. See [the scoped capability matrix](MYSQL_FIDELITY.md); this covers new-table DDL on MySQL 8.4 / InnoDB, not all engines, MariaDB versions, other format mappings, or migrations.
+
+A06–A07 verification (2026-10-12): live MySQL 8.4.11 tests compare source/target `SHOW CREATE TABLE` definitions (normalizing temporary target suffixes and ordinary-index display order), re-read the target, and verify FK/check enforcement and binary/bit/multiline/backslash/default values. The suite covers composite/functional unique keys, reverse table dependency order, generated/check/index expressions containing SQL literals, precision, unsigned ranges, and multiple FKs to the same target. It exposed and fixed truncated binary defaults in `information_schema` by extracting native defaults from SQL-aware `SHOW CREATE TABLE` definitions. Native SHOW CREATE also avoids stale auto-increment statistics, and escaped catalog expressions are decoded before rendering. Unsupported views/triggers/partitioned tables produce warnings and strict failures; strict failure preserves existing files and happens before opening an output connection. CLI dry-run and per-job strict options are tested. The MySQL container test runner now selects reader/writer packages by default. `go test -mod=vendor -p 1 ./...` passed with `RELSPEC_TEST_MYSQL_CONN` configured; `go vet -mod=vendor ./...`, CLI strict/dry-run checks, shell syntax, and `git diff --check` passed. The MySQL container runner also passed using its schema-scoped account; its disposable server enables trigger-fixture creation after final-server readiness. PostgreSQL and SQL Server live variables were unset for this batch. Checks used `go1.27.1-X:nodwarf5 linux/amd64`; declared-minimum-toolchain coverage remains A13 work. Disposable MySQL instances were removed after verification. A08 now also has live MySQL coverage for embedded statement delimiters/default contents.
+
 A05–A08 verification: unit regressions and live PostgreSQL 18 checks cover unusual names, comments/defaults, rerunnable file/statement output, diff migrations, sequences, primary-key replacement, audit functions/triggers, and both standard-string modes. MySQL statement preservation is unit-tested; a live MySQL instance was not used for A08. `go test -mod=vendor -p 1 ./...` passed with `RELSPEC_TEST_PG_CONN` set to the disposable instance; `go vet -mod=vendor ./...`, executable CLI help checks, and `git diff --check` passed. SQL Server tests were not configured for this batch. The disposable instance was removed after verification.
 
 Additional observation: a parallel live full-suite run hit a PostgreSQL reader catalog race (`could not open relation with OID`) while another package's test dropped schema objects. The writer safely fell back to full DDL and its preflight still stopped all mutations, but the existing test assumed no successful read-only preflights before failure. Running live packages serially passed. Reader resilience to concurrent catalog changes remains outside A05/A08; A10 specifically concerns cancellation/timeouts.
@@ -155,6 +160,8 @@ PostgreSQL documents the distinct identifier, string, and dollar-quote rules in
 
 ### A06 — MySQL constraint reading scans nullable metadata into strings
 
+**Repair status: addressed.** Nullable metadata scans and qualified queries are covered by live MySQL 8.4 round trips with primary, unique, composite FK, and functional-index definitions.
+
 **P1 / High · Database · Code-confirmed; live MySQL not exercised**
 
 Evidence: `pkg/readers/mysql/reader.go:181–220`, specifically the `rs`, `rt`, and `rc` string variables passed to `rows.Scan`.
@@ -169,6 +176,8 @@ Reference: [MySQL KEY_COLUMN_USAGE documentation](https://dev.mysql.com/doc/refm
 
 ### A07 — MySQL conversion silently loses constraints, indexes, and type detail
 
+**Repair status: addressed within the [documented MySQL table-schema contract](MYSQL_FIDELITY.md).** Supported features survive live round trips through JSON/YAML; known unsupported modeled/discovered features produce diagnostics or strict conversion failures. MySQL output remains creation DDL for existing databases, with engine/version/SQL-mode limits stated in the capability matrix.
+
 **P1 / High · Database · Reproduced omissions; additional losses code-confirmed**
 
 Evidence: `pkg/writers/mysql/writer.go:96–163`; `pkg/readers/mysql/reader.go:153–178`; `pkg/mariadb/datatypes.go`.

pkg/jobs/jobs.go

@@ -277,6 +277,7 @@ func parseHumanSize(s string) (int64, error) {
 
 // Options carries the subset of command flags a job file may set.
 type Options struct {
+	StrictConversion     bool   `yaml:"strict_conversion"`
 	LowercaseIdentifiers bool   `yaml:"lowercase_identifiers"`
 	FlattenSchema        bool   `yaml:"flatten_schema"`
 	Schema               string `yaml:"schema"`

pkg/mariadb/datatypes.go

@@ -61,6 +61,7 @@ var MariaDBToCanonicalTypes = map[string]string{
 // CanonicalToMariaDBTypes maps canonical types to MariaDB/MySQL types.
 var CanonicalToMariaDBTypes = map[string]string{
 	"bool":        "TINYINT(1)",
+	"boolean":     "TINYINT(1)",
 	"int8":        "TINYINT",
 	"int16":       "SMALLINT",
 	"int":         "INT",
@@ -114,22 +115,28 @@ func NormalizeMariaDBType(baseType string) string {
 // ConvertMariaDBToCanonical converts a MariaDB/MySQL type name to the canonical type.
 // Strips dimension parameters and normalizes aliases. Defaults to "string".
 func ConvertMariaDBToCanonical(mariadbType string) string {
-	base := strings.ToLower(strings.TrimSpace(mariadbType))
+	lower := strings.ToLower(strings.TrimSpace(mariadbType))
-	if idx := strings.Index(base, "("); idx >= 0 {
+	base := lower
-		base = strings.TrimSpace(base[:idx])
+	if idx := strings.IndexAny(base, "( "); idx >= 0 {
+		base = base[:idx]
+	}
+	canonical, ok := MariaDBToCanonicalTypes[base]
+	if ok {
+		if strings.Contains(lower, "unsigned") || strings.Contains(lower, "zerofill") {
+			switch canonical {
+			case "int8":
+				return "uint8"
+			case "int16":
+				return "uint16"
+			case "int":
+				return "uint"
+			case "int64":
+				return "uint64"
+			}
 		}
-
-	if canonical, ok := MariaDBToCanonicalTypes[base]; ok {
 		return canonical
 	}
 
-	// Prefix match for composite types (e.g., "unsigned bigint")
-	for key, canonical := range MariaDBToCanonicalTypes {
-		if strings.HasPrefix(base, key) {
-			return canonical
-		}
-	}
-
 	return "string"
 }
 
@@ -145,12 +152,5 @@ func ConvertCanonicalToMariaDB(canonicalType string) string {
 		return mariadbType
 	}
 
-	// Prefix fallback
-	for canonical, mariadb := range CanonicalToMariaDBTypes {
-		if strings.HasPrefix(lower, canonical) {
-			return mariadb
-		}
-	}
-
 	return "VARCHAR(255)"
 }

pkg/mariadb/datatypes_test.go

@@ -0,0 +1,13 @@
+package mariadb
+
+import "testing"
+
+func TestIntegerSignedness(t *testing.T) {
+	for _, tc := range []struct{ input, want string }{
+		{"tinyint(3) unsigned", "uint8"}, {"smallint unsigned", "uint16"}, {"mediumint unsigned", "uint"}, {"int unsigned", "uint"}, {"bigint unsigned", "uint64"}, {"bigint zerofill", "uint64"}, {"bigint", "int64"}, {"varchar(32)", "string"},
+	} {
+		if got := ConvertMariaDBToCanonical(tc.input); got != tc.want {
+			t.Errorf("%s: got %s want %s", tc.input, got, tc.want)
+		}
+	}
+}

pkg/models/models.go

@@ -256,9 +256,19 @@ func (d *Column) SQLName() string {
 	return strings.ToLower(d.Name)
 }
 
+// IndexPart is an ordered MySQL index key part. Name and Expression are mutually
+// exclusive; expressions are executable SQL and are not identifier-normalized.
+type IndexPart struct {
+	Name       string `json:"name,omitempty" yaml:"name,omitempty" xml:"name,omitempty"`
+	Expression string `json:"expression,omitempty" yaml:"expression,omitempty" xml:"expression,omitempty"`
+	Length     int    `json:"length,omitempty" yaml:"length,omitempty" xml:"length,omitempty"`
+	Descending bool   `json:"descending,omitempty" yaml:"descending,omitempty" xml:"descending,omitempty"`
+}
+
 // Index represents a database index for optimizing query performance.
 // Indexes can be unique, partial, or include additional columns.
 type Index struct {
+	KeyParts    []IndexPart    `json:"key_parts,omitempty" yaml:"key_parts,omitempty" xml:"key_parts,omitempty"`
 	Name        string         `json:"name" yaml:"name" xml:"name"`
 	Description string         `json:"description,omitempty" yaml:"description,omitempty" xml:"description,omitempty"`
 	Table       string         `json:"table,omitempty" yaml:"table,omitempty" xml:"table,omitempty"`
@@ -318,6 +328,7 @@ func (d *Relationship) SQLName() string {
 // Constraint represents a database constraint that enforces data integrity rules.
 // Constraints can be primary keys, foreign keys, unique constraints, check constraints, or not-null constraints.
 type Constraint struct {
+	Metadata          map[string]any `json:"metadata,omitempty" yaml:"metadata,omitempty" xml:"-"`
 	Name              string         `json:"name" yaml:"name" xml:"name"`
 	Type              ConstraintType `json:"type" yaml:"type" xml:"type"`
 	Columns           []string       `json:"columns" yaml:"columns" xml:"columns"`

pkg/readers/mysql/defaults.go

@@ -0,0 +1,194 @@
+package mysql
+
+import (
+	"regexp"
+	"strings"
+)
+
+// columnDefaults extracts native DEFAULT expressions from SHOW CREATE TABLE.
+// MySQL can truncate binary defaults in information_schema (for example X'00FF'
+// appears as just "0x"). SHOW CREATE is authoritative for their SQL spelling.
+// Separators and whitespace inside quoted strings, identifiers and nested
+// expressions are never treated as definition/default boundaries.
+func columnDefaults(create string) map[string]string {
+	out := map[string]string{}
+	depth, start := 0, 0
+	var quoted byte
+	definitions := []string{}
+	for i := 0; i < len(create); i++ {
+		ch := create[i]
+		if quoted != 0 {
+			if ch == '\\' && quoted != '`' && i+1 < len(create) {
+				i++
+				continue
+			}
+			if ch == quoted {
+				if i+1 < len(create) && create[i+1] == quoted {
+					i++
+				} else {
+					quoted = 0
+				}
+			}
+			continue
+		}
+		if ch == '\'' || ch == '"' || ch == '`' {
+			quoted = ch
+			continue
+		}
+		switch ch {
+		case '(':
+			depth++
+			if depth == 1 {
+				start = i + 1
+			}
+		case ',':
+			if depth == 1 {
+				definitions = append(definitions, create[start:i])
+				start = i + 1
+			}
+		case ')':
+			depth--
+			if depth == 0 {
+				definitions = append(definitions, create[start:i])
+				break
+			}
+		}
+		if ch == ')' && depth == 0 {
+			break
+		}
+	}
+	for _, def := range definitions {
+		def = strings.TrimSpace(def)
+		if len(def) == 0 || def[0] != '`' {
+			continue
+		}
+		var name strings.Builder
+		end := 1
+		for end < len(def) {
+			if def[end] == '`' {
+				if end+1 < len(def) && def[end+1] == '`' {
+					name.WriteByte('`')
+					end += 2
+					continue
+				}
+				end++
+				break
+			}
+			name.WriteByte(def[end])
+			end++
+		}
+		// Consume full tokens so DEFAULT inside a generated expression or literal
+		// cannot masquerade as a column default.
+		for end < len(def) {
+			for end < len(def) && isSpace(def[end]) {
+				end++
+			}
+			begin := end
+			end = tokenEnd(def, end)
+			if end == begin {
+				break
+			}
+			if strings.EqualFold(def[begin:end], "DEFAULT") {
+				for end < len(def) && isSpace(def[end]) {
+					end++
+				}
+				finish := tokenEnd(def, end)
+				out[name.String()] = def[end:finish]
+				break
+			}
+		}
+	}
+	return out
+}
+func isSpace(b byte) bool { return b == ' ' || b == '\n' || b == '\r' || b == '\t' }
+func tokenEnd(s string, start int) int {
+	depth := 0
+	var quoted byte
+	for i := start; i < len(s); i++ {
+		ch := s[i]
+		if quoted != 0 {
+			if ch == '\\' && quoted != '`' && i+1 < len(s) {
+				i++
+				continue
+			}
+			if ch == quoted {
+				if i+1 < len(s) && s[i+1] == quoted {
+					i++
+				} else {
+					quoted = 0
+				}
+			}
+			continue
+		}
+		if ch == '\'' || ch == '"' || ch == '`' {
+			quoted = ch
+			continue
+		}
+		if ch == '(' {
+			depth++
+		}
+		if ch == ')' {
+			depth--
+		}
+		if depth == 0 && isSpace(ch) {
+			return i
+		}
+	}
+	return len(s)
+}
+
+// SHOW CREATE has native options not exposed by STATISTICS/COLUMNS. Ignore
+// quoted identifiers and values when detecting options outside our contract.
+func unquotedSQL(create string) string {
+	var code strings.Builder
+	var quoted byte
+	for i := 0; i < len(create); i++ {
+		ch := create[i]
+		if quoted != 0 {
+			if ch == '\\' && quoted != '`' && i+1 < len(create) {
+				i++
+				continue
+			}
+			if ch == quoted {
+				if i+1 < len(create) && create[i+1] == quoted {
+					i++
+				} else {
+					quoted = 0
+					code.WriteByte(' ')
+				}
+			}
+			continue
+		}
+		if ch == '\'' || ch == '"' || ch == '`' {
+			quoted = ch
+			code.WriteByte(' ')
+			continue
+		}
+		code.WriteByte(ch)
+	}
+	return code.String()
+}
+
+var autoIncrementOption = regexp.MustCompile(`(?i)\bAUTO_INCREMENT\s*=\s*([0-9]+)`)
+
+func autoIncrementValue(create string) string {
+	if match := autoIncrementOption.FindStringSubmatch(unquotedSQL(create)); len(match) > 1 {
+		return match[1]
+	}
+	return "1"
+}
+func unsupportedNativeOptions(create string) []string {
+	words := strings.FieldsFunc(strings.ToUpper(unquotedSQL(create)), func(r rune) bool { return !(r >= 'A' && r <= 'Z' || r == '_') })
+	var out []string
+	for i, w := range words {
+		switch w {
+		case "ENGINE_ATTRIBUTE", "SECONDARY_ENGINE_ATTRIBUTE", "KEY_BLOCK_SIZE", "COLUMN_FORMAT", "STORAGE":
+			out = append(out, w)
+		case "PARSER":
+			if i > 0 && words[i-1] == "WITH" {
+				out = append(out, "WITH PARSER")
+			}
+		}
+	}
+	return out
+}

pkg/readers/mysql/expressions_test.go

@@ -0,0 +1,54 @@
+package mysql
+
+import "testing"
+
+func TestUnescapeExpression(t *testing.T) {
+	for _, tc := range []struct{ input, want string }{
+		{`_utf8mb4\'one\\ntwo\'`, `_utf8mb4'one\ntwo'`},
+		{`concat(\'don\\\'t\',\' change\')`, `concat('don\'t',' change')`},
+		{`(uuid())`, `(uuid())`},
+	} {
+		if got := unescapeExpression(tc.input); got != tc.want {
+			t.Errorf("%q: got %q want %q", tc.input, got, tc.want)
+		}
+	}
+}
+
+func TestNativeColumnDefaults(t *testing.T) {
+	create := "CREATE TABLE `odd(table` (\n" +
+		" `a,b` varbinary(8) DEFAULT 0x0027FF,\n" +
+		" `tick``name` varchar(30) DEFAULT 'don''t, (split)',\n" +
+		" `expr` varchar(30) DEFAULT (concat('DEFAULT, ', (uuid()))),\n" +
+		" `generated` varchar(30) GENERATED ALWAYS AS (concat('DEFAULT',`expr`)) VIRTUAL,\n" +
+		" `new\nline` int DEFAULT 3,\n" +
+		" PRIMARY KEY (`a,b`)\n) ENGINE=InnoDB"
+	got := columnDefaults(create)
+	want := map[string]string{"a,b": "0x0027FF", "tick`name": "'don''t, (split)'", "expr": "(concat('DEFAULT, ', (uuid())))", "new\nline": "3"}
+	if len(got) != len(want) {
+		t.Fatalf("defaults: %v", got)
+	}
+	for name, value := range want {
+		if got[name] != value {
+			t.Errorf("%s: got %q want %q", name, got[name], value)
+		}
+	}
+}
+
+func TestNativeOptionsIgnoreQuotedValues(t *testing.T) {
+	create := "CREATE TABLE `WITH PARSER` (`STORAGE` int COMMENT 'KEY_BLOCK_SIZE', KEY `ENGINE_ATTRIBUTE` (`STORAGE`) WITH PARSER `ngram`) ENGINE=InnoDB"
+	options := unsupportedNativeOptions(create)
+	if len(options) != 1 || options[0] != "WITH PARSER" {
+		t.Fatalf("native options: %v", options)
+	}
+}
+
+func TestNativeAutoIncrementIgnoresQuotedValues(t *testing.T) {
+	for _, tc := range []struct{ create, want string }{
+		{"CREATE TABLE `x` (`id` bigint AUTO_INCREMENT) ENGINE=InnoDB AUTO_INCREMENT=18446744073709551615", "18446744073709551615"},
+		{"CREATE TABLE `x` (`id` bigint AUTO_INCREMENT) COMMENT='AUTO_INCREMENT=12'", "1"},
+	} {
+		if got := autoIncrementValue(tc.create); got != tc.want {
+			t.Errorf("got %s want %s", got, tc.want)
+		}
+	}
+}

pkg/readers/mysql/reader.go

@@ -4,9 +4,10 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"regexp"
 	"strings"
 
-	_ "github.com/go-sql-driver/mysql"
+	mysqlDriver "github.com/go-sql-driver/mysql"
 
 	"git.warky.dev/wdevs/relspecgo/pkg/mariadb"
 	"git.warky.dev/wdevs/relspecgo/pkg/models"
@@ -31,12 +32,13 @@ func (r *Reader) ReadDatabase() (*models.Database, error) {
 		return nil, fmt.Errorf("failed to connect: %w", err)
 	}
 	defer r.close()
-	var name, version string
+	var name, version, sqlMode string
-	if err := r.db.QueryRowContext(r.ctx, "SELECT DATABASE()").Scan(&name); err != nil {
+	if err := r.db.QueryRowContext(r.ctx, "SELECT DATABASE(), @@SESSION.sql_mode").Scan(&name, &sqlMode); err != nil {
 		return nil, fmt.Errorf("failed to get database name: %w", err)
 	}
 	_ = r.db.QueryRowContext(r.ctx, "SELECT VERSION()").Scan(&version)
 	db := models.InitDatabase(name)
+	db.Metadata["mysql_sql_mode"] = sqlMode
 	db.DatabaseType, db.SourceFormat, db.DatabaseVersion = models.MySQLDatabaseType, "mysql", version
 	schemas, err := r.querySchemas(name)
 	if err != nil {
@@ -48,8 +50,10 @@ func (r *Reader) ReadDatabase() (*models.Database, error) {
 			return nil, err
 		}
 		schema.Tables = tables
+		schema.Metadata["mysql_sql_mode"] = sqlMode
 		for _, table := range tables {
-			table.Columns, err = r.queryColumns(schema.Name, table.Name)
+			table.Metadata["mysql_sql_mode"] = sqlMode
+			table.Columns, err = r.queryColumns(schema.Name, table)
 			if err != nil {
 				return nil, err
 			}
@@ -62,6 +66,15 @@ func (r *Reader) ReadDatabase() (*models.Database, error) {
 				return nil, err
 			}
 			table.RefSchema = schema
+			for _, c := range table.Constraints {
+				if c.Type == models.PrimaryKeyConstraint {
+					for _, n := range c.Columns {
+						if col := table.Columns[n]; col != nil {
+							col.IsPrimaryKey = true
+						}
+					}
+				}
+			}
 			for _, c := range table.Constraints {
 				if c.Type == models.ForeignKeyConstraint {
 					r.deriveRelationship(table, c)
@@ -71,6 +84,9 @@ func (r *Reader) ReadDatabase() (*models.Database, error) {
 		schema.RefDatabase = db
 		db.Schemas = append(db.Schemas, schema)
 	}
+	if err := r.readUnsupported(db, name); err != nil {
+		return nil, err
+	}
 	return db, nil
 }
 
@@ -97,7 +113,17 @@ func (r *Reader) ReadTable() (*models.Table, error) {
 }
 
 func (r *Reader) connect() error {
-	db, err := sql.Open("mysql", r.options.ConnectionString)
+	cfg, err := mysqlDriver.ParseDSN(r.options.ConnectionString)
+	if err != nil {
+		return err
+	}
+	if cfg.Params == nil {
+		cfg.Params = map[string]string{}
+	}
+	// SHOW CREATE parsing requires quoted column identifiers, including when the
+	// caller's metadata connection would otherwise disable show-create quoting.
+	cfg.Params["sql_quote_show_create"] = "1"
+	db, err := sql.Open("mysql", cfg.FormatDSN())
 	if err != nil {
 		return err
 	}
@@ -134,61 +160,147 @@ func (r *Reader) querySchemas(current string) ([]*models.Schema, error) {
 }
 
 func (r *Reader) queryTables(schema string) ([]*models.Table, error) {
-	rows, err := r.db.QueryContext(r.ctx, "SELECT TABLE_NAME FROM information_schema.TABLES WHERE TABLE_SCHEMA = ? AND TABLE_TYPE = 'BASE TABLE' ORDER BY TABLE_NAME", schema)
+	rows, err := r.db.QueryContext(r.ctx, "SELECT TABLE_NAME, ENGINE, TABLE_COLLATION, TABLE_COMMENT, CREATE_OPTIONS, AUTO_INCREMENT FROM information_schema.TABLES WHERE TABLE_SCHEMA = ? AND TABLE_TYPE = 'BASE TABLE' ORDER BY TABLE_NAME", schema)
 	if err != nil {
 		return nil, err
 	}
 	defer rows.Close()
 	var out []*models.Table
 	for rows.Next() {
-		var n string
+		var n, engine, collation, comment, options string
-		if err := rows.Scan(&n); err != nil {
+		var auto sql.NullString
+		if err := rows.Scan(&n, &engine, &collation, &comment, &options, &auto); err != nil {
 			return nil, err
 		}
-		out = append(out, models.InitTable(n, schema))
+		t := models.InitTable(n, schema)
+		t.Comment = comment
+		t.Metadata["mysql_engine"], t.Metadata["mysql_collation"], t.Metadata["mysql_create_options"] = engine, collation, options
+		if auto.Valid {
+			t.Metadata["mysql_auto_increment"] = auto.String
+		}
+		out = append(out, t)
 	}
 	return out, rows.Err()
 }
 
-func (r *Reader) queryColumns(schema, table string) (map[string]*models.Column, error) {
+var onUpdateExtra = regexp.MustCompile(`on update current_timestamp(?:\(\d*\))?`)
-	rows, err := r.db.QueryContext(r.ctx, `SELECT COLUMN_NAME, COLUMN_TYPE, IS_NULLABLE, COLUMN_DEFAULT, ORDINAL_POSITION, EXTRA, COLUMN_COMMENT FROM information_schema.COLUMNS WHERE TABLE_SCHEMA = ? AND TABLE_NAME = ? ORDER BY ORDINAL_POSITION`, schema, table)
+
+func (r *Reader) queryColumns(schema string, table *models.Table) (map[string]*models.Column, error) {
+	rows, err := r.db.QueryContext(r.ctx, `SELECT COLUMN_NAME, COLUMN_TYPE, IS_NULLABLE, COLUMN_DEFAULT, ORDINAL_POSITION, EXTRA, COLUMN_COMMENT,
+ CHARACTER_MAXIMUM_LENGTH, NUMERIC_PRECISION, NUMERIC_SCALE, DATETIME_PRECISION, COLLATION_NAME, CHARACTER_SET_NAME, GENERATION_EXPRESSION, SRS_ID
+ FROM information_schema.COLUMNS WHERE TABLE_SCHEMA=? AND TABLE_NAME=? ORDER BY ORDINAL_POSITION`, schema, table.Name)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("columns %s.%s: %w", schema, table.Name, err)
 	}
 	defer rows.Close()
 	out := map[string]*models.Column{}
 	for rows.Next() {
 		var name, typ, nullable, extra, comment string
-		var def sql.NullString
+		var def, collation, charset, generation sql.NullString
+		var length, precision, scale, datetime, srid sql.NullInt64
 		var pos int
-		if err := rows.Scan(&name, &typ, &nullable, &def, &pos, &extra, &comment); err != nil {
+		if err := rows.Scan(&name, &typ, &nullable, &def, &pos, &extra, &comment, &length, &precision, &scale, &datetime, &collation, &charset, &generation, &srid); err != nil {
 			return nil, err
 		}
-		c := models.InitColumn(name, table, schema)
+		c := models.InitColumn(name, table.Name, schema)
-		c.Type = r.mapDataType(typ)
+		c.Type, c.NotNull, c.Sequence, c.Comment = r.mapDataType(typ), nullable == "NO", uint(pos), comment
-		c.NotNull = strings.EqualFold(nullable, "NO")
+		// The native declaration preserves mediumint, enum/set, binary/blob sizes,
-		c.Sequence = uint(pos)
+		// unsigned/zerofill and timestamp versus datetime. Canonical dimensions remain editable.
-		c.Comment = comment
+		c.Length, c.Precision, c.Scale = int(length.Int64), int(precision.Int64), int(scale.Int64)
+		if datetime.Valid {
+			c.Precision = int(datetime.Int64)
+		}
+		c.Collation = collation.String
+		c.Metadata["mysql_type"] = typ
+		c.Metadata["mysql_type_signature"] = typeSignature(c)
+		c.Metadata["mysql_charset"] = charset.String
+		c.Metadata["mysql_datetime_precision"] = datetime.Int64
+		c.Metadata["mysql_default_expression"] = strings.Contains(extra, "DEFAULT_GENERATED") || strings.HasPrefix(strings.ToLower(def.String), "current_timestamp") && (c.Type == "timestamp")
 		if def.Valid {
 			c.Default = def.String
+			if strings.Contains(extra, "DEFAULT_GENERATED") {
+				c.Default = unescapeExpression(def.String)
+			}
+			if strings.HasPrefix(typ, "bit(") && def.Valid {
+				c.Metadata["mysql_default_expression"] = true
+			}
+		}
+		c.AutoIncrement = strings.Contains(extra, "auto_increment")
+		c.Generated, c.GenerationExpression = generation.String != "", unescapeExpression(generation.String)
+		if strings.Contains(extra, "STORED GENERATED") {
+			c.Metadata["mysql_generation_storage"] = "STORED"
+		} else if c.Generated {
+			c.Metadata["mysql_generation_storage"] = "VIRTUAL"
+		}
+		c.Metadata["mysql_invisible"] = strings.Contains(extra, "INVISIBLE")
+		remaining := onUpdateExtra.ReplaceAllString(strings.ToLower(extra), "")
+		for _, known := range []string{"auto_increment", "default_generated", "stored generated", "virtual generated", "invisible"} {
+			remaining = strings.ReplaceAll(remaining, known, "")
+		}
+		if remaining = strings.TrimSpace(remaining); remaining != "" {
+			c.Metadata["mysql_unsupported_extra"] = remaining
+		}
+		if i := strings.Index(strings.ToLower(extra), "on update "); i >= 0 {
+			c.Metadata["mysql_on_update"] = strings.Fields(extra[i+10:])[0]
+		}
+		if srid.Valid {
+			c.Metadata["mysql_srs_id"] = srid.Int64
 		}
-		c.AutoIncrement = strings.Contains(strings.ToLower(extra), "auto_increment")
 		out[name] = c
 	}
-	return out, rows.Err()
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	var tableName, create string
+	qualified := "`" + strings.ReplaceAll(schema, "`", "``") + "`.`" + strings.ReplaceAll(table.Name, "`", "``") + "`"
+	if err := r.db.QueryRowContext(r.ctx, "SHOW CREATE TABLE "+qualified).Scan(&tableName, &create); err != nil {
+		return nil, fmt.Errorf("native defaults %s.%s: %w", schema, table.Name, err)
+	}
+	// information_schema AUTO_INCREMENT may be stale because of statistics caching.
+	for _, c := range out {
+		if c.AutoIncrement {
+			table.Metadata["mysql_auto_increment"] = autoIncrementValue(create)
+			break
+		}
+	}
+	if options := unsupportedNativeOptions(create); len(options) > 0 {
+		table.Metadata["mysql_unsupported_options"] = strings.Join(options, ", ")
+	}
+	for name, sql := range columnDefaults(create) {
+		c := out[name]
+		if c == nil || c.Default == nil {
+			continue
+		}
+		if c.Type == "bytea" {
+			c.Default = sql
+		}
+		c.Metadata["mysql_default_sql"] = sql
+		c.Metadata["mysql_default_value"] = fmt.Sprint(c.Default)
+	}
+	return out, nil
+}
+
+func typeSignature(c *models.Column) string {
+	return fmt.Sprintf("%s/%d/%d/%d", c.Type, c.Length, c.Precision, c.Scale)
 }
 
 func (r *Reader) queryConstraints(schema, table string) (map[string]*models.Constraint, error) {
-	rows, err := r.db.QueryContext(r.ctx, `SELECT CONSTRAINT_NAME, CONSTRAINT_TYPE, COLUMN_NAME, REFERENCED_TABLE_SCHEMA, REFERENCED_TABLE_NAME, REFERENCED_COLUMN_NAME, ORDINAL_POSITION FROM information_schema.KEY_COLUMN_USAGE k JOIN information_schema.TABLE_CONSTRAINTS t USING (CONSTRAINT_SCHEMA, TABLE_NAME, CONSTRAINT_NAME) WHERE k.TABLE_SCHEMA=? AND k.TABLE_NAME=? ORDER BY CONSTRAINT_NAME, ORDINAL_POSITION`, schema, table)
+	rows, err := r.db.QueryContext(r.ctx, `SELECT k.CONSTRAINT_NAME, t.CONSTRAINT_TYPE, k.COLUMN_NAME,
+ k.REFERENCED_TABLE_SCHEMA, k.REFERENCED_TABLE_NAME, k.REFERENCED_COLUMN_NAME, k.ORDINAL_POSITION,
+ rc.DELETE_RULE, rc.UPDATE_RULE FROM information_schema.KEY_COLUMN_USAGE k
+ JOIN information_schema.TABLE_CONSTRAINTS t USING (CONSTRAINT_SCHEMA,TABLE_NAME,CONSTRAINT_NAME)
+ LEFT JOIN information_schema.REFERENTIAL_CONSTRAINTS rc ON rc.CONSTRAINT_SCHEMA=k.CONSTRAINT_SCHEMA AND rc.TABLE_NAME=k.TABLE_NAME AND rc.CONSTRAINT_NAME=k.CONSTRAINT_NAME
+ WHERE k.TABLE_SCHEMA=? AND k.TABLE_NAME=? ORDER BY k.CONSTRAINT_NAME,k.ORDINAL_POSITION`, schema, table)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("constraints %s.%s: %w", schema, table, err)
 	}
-	defer rows.Close()
 	out := map[string]*models.Constraint{}
 	for rows.Next() {
-		var name, typ, col, rs, rt, rc string
+		var name, typ string
+		var col, rs, rt, rc, del, upd sql.NullString
 		var pos int
-		if err := rows.Scan(&name, &typ, &col, &rs, &rt, &rc, &pos); err != nil {
+		if err := rows.Scan(&name, &typ, &col, &rs, &rt, &rc, &pos, &del, &upd); err != nil {
+			rows.Close()
 			return nil, err
 		}
 		c := out[name]
@@ -201,31 +313,54 @@ func (r *Reader) queryConstraints(schema, table string) (map[string]*models.Cons
 				ct = models.ForeignKeyConstraint
 			}
 			c = models.InitConstraint(name, ct)
-			c.Schema = schema
+			c.Schema, c.Table = schema, table
-			c.Table = table
+			c.ReferencedSchema, c.ReferencedTable = rs.String, rt.String
-			c.ReferencedSchema = rs
+			c.OnDelete, c.OnUpdate = del.String, upd.String
-			c.ReferencedTable = rt
 			out[name] = c
 		}
-		c.Columns = append(c.Columns, col)
+		if col.Valid {
-		if rc != "" {
+			c.Columns = append(c.Columns, col.String)
-			c.ReferencedColumns = append(c.ReferencedColumns, rc)
 		}
+		if rc.Valid {
+			c.ReferencedColumns = append(c.ReferencedColumns, rc.String)
+		}
+	}
+	err = rows.Err()
+	rows.Close()
+	if err != nil {
+		return nil, err
+	}
+	rows, err = r.db.QueryContext(r.ctx, `SELECT t.CONSTRAINT_NAME,c.CHECK_CLAUSE,t.ENFORCED FROM information_schema.TABLE_CONSTRAINTS t JOIN information_schema.CHECK_CONSTRAINTS c USING (CONSTRAINT_SCHEMA,CONSTRAINT_NAME) WHERE t.TABLE_SCHEMA=? AND t.TABLE_NAME=? AND t.CONSTRAINT_TYPE='CHECK' ORDER BY t.CONSTRAINT_NAME`, schema, table)
+	if err != nil {
+		return nil, fmt.Errorf("checks %s.%s (requires MySQL 8.0.16+): %w", schema, table, err)
+	}
+	defer rows.Close()
+	for rows.Next() {
+		var name, expr, enforced string
+		if err := rows.Scan(&name, &expr, &enforced); err != nil {
+			return nil, err
+		}
+		c := models.InitConstraint(name, models.CheckConstraint)
+		c.Schema, c.Table, c.Expression = schema, table, unescapeExpression(expr)
+		c.Metadata = map[string]any{"mysql_enforced": enforced == "YES"}
+		out[name] = c
 	}
 	return out, rows.Err()
 }
 
 func (r *Reader) queryIndexes(schema, table string) (map[string]*models.Index, error) {
-	rows, err := r.db.QueryContext(r.ctx, `SELECT INDEX_NAME, NON_UNIQUE, COLUMN_NAME, SEQ_IN_INDEX, INDEX_TYPE FROM information_schema.STATISTICS WHERE TABLE_SCHEMA=? AND TABLE_NAME=? AND INDEX_NAME <> 'PRIMARY' ORDER BY INDEX_NAME, SEQ_IN_INDEX`, schema, table)
+	rows, err := r.db.QueryContext(r.ctx, `SELECT INDEX_NAME, NON_UNIQUE, COLUMN_NAME, SEQ_IN_INDEX, INDEX_TYPE, EXPRESSION, SUB_PART, COLLATION, IS_VISIBLE, INDEX_COMMENT FROM information_schema.STATISTICS WHERE TABLE_SCHEMA=? AND TABLE_NAME=? ORDER BY INDEX_NAME,SEQ_IN_INDEX`, schema, table)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("indexes %s.%s (requires MySQL 8.0.13+): %w", schema, table, err)
 	}
 	defer rows.Close()
 	out := map[string]*models.Index{}
 	for rows.Next() {
-		var name, col, typ string
+		var name, typ, visible, comment string
+		var col, expr, direction sql.NullString
+		var prefix sql.NullInt64
 		var non, seq int
-		if err := rows.Scan(&name, &non, &col, &seq, &typ); err != nil {
+		if err := rows.Scan(&name, &non, &col, &seq, &typ, &expr, &prefix, &direction, &visible, &comment); err != nil {
 			return nil, err
 		}
 		i := out[name]
@@ -233,22 +368,96 @@ func (r *Reader) queryIndexes(schema, table string) (map[string]*models.Index, e
 			i = models.InitIndex(name, table, schema)
 			i.Unique = non == 0
 			i.Type = strings.ToLower(typ)
+			i.Comment = comment
+			i.Metadata["mysql_visible"] = visible == "YES"
 			out[name] = i
 		}
-		i.Columns = append(i.Columns, col)
+		i.Columns = append(i.Columns, col.String)
+		i.KeyParts = append(i.KeyParts, models.IndexPart{Name: col.String, Expression: unescapeExpression(expr.String), Length: int(prefix.Int64), Descending: direction.String == "D"})
 	}
 	return out, rows.Err()
 }
 
+// Record objects outside the supported table-schema contract rather than silently
+// discarding them. Writers can warn or reject the conversion before any output.
+func (r *Reader) readUnsupported(db *models.Database, schema string) error {
+	queries := []struct{ kind, sql string }{
+		{"view", `SELECT TABLE_NAME FROM information_schema.VIEWS WHERE TABLE_SCHEMA=?`},
+		{"trigger", `SELECT TRIGGER_NAME FROM information_schema.TRIGGERS WHERE TRIGGER_SCHEMA=?`},
+		{"routine", `SELECT ROUTINE_NAME FROM information_schema.ROUTINES WHERE ROUTINE_SCHEMA=?`},
+		{"event", `SELECT EVENT_NAME FROM information_schema.EVENTS WHERE EVENT_SCHEMA=?`},
+		{"partitioned table", `SELECT DISTINCT TABLE_NAME FROM information_schema.PARTITIONS WHERE TABLE_SCHEMA=? AND PARTITION_NAME IS NOT NULL`},
+	}
+	var unsupported []string
+	for _, q := range queries {
+		rows, err := r.db.QueryContext(r.ctx, q.sql, schema)
+		if err != nil {
+			return fmt.Errorf("discover %s: %w", q.kind, err)
+		}
+		for rows.Next() {
+			var name string
+			if err := rows.Scan(&name); err != nil {
+				rows.Close()
+				return err
+			}
+			unsupported = append(unsupported, q.kind+" "+schema+"."+name)
+		}
+		err = rows.Err()
+		rows.Close()
+		if err != nil {
+			return err
+		}
+	}
+	if len(unsupported) > 0 {
+		db.Metadata["mysql_unsupported"] = unsupported
+		for _, s := range db.Schemas {
+			s.Metadata["mysql_unsupported"] = unsupported
+		}
+		if r.options.Progress != nil {
+			for _, item := range unsupported {
+				r.options.Progress("warning: unsupported MySQL " + item)
+			}
+		}
+	}
+	return nil
+}
+
 func (r *Reader) deriveRelationship(t *models.Table, c *models.Constraint) {
-	n := fmt.Sprintf("%s_to_%s", t.Name, c.ReferencedTable)
+	n := fmt.Sprintf("%s_%s", t.Name, c.Name)
 	rel := models.InitRelationship(n, models.OneToMany)
-	rel.FromTable = t.Name
+	rel.FromTable, rel.FromSchema = t.Name, t.Schema
-	rel.FromSchema = t.Schema
 	rel.FromColumns = append([]string(nil), c.Columns...)
-	rel.ToTable = c.ReferencedTable
+	rel.ToTable, rel.ToSchema = c.ReferencedTable, c.ReferencedSchema
-	rel.ToSchema = c.ReferencedSchema
 	rel.ToColumns = append([]string(nil), c.ReferencedColumns...)
 	rel.ForeignKey = c.Name
 	t.Relationships[n] = rel
 }
+
+// MySQL information_schema escapes SQL expressions by an additional layer
+// (including quote delimiters). This covers defaults, generated columns, checks,
+// and functional indexes. Literal defaults are already values and bypass this.
+func unescapeExpression(s string) string {
+	var out strings.Builder
+	for i := 0; i < len(s); i++ {
+		if s[i] == '\\' && i+1 < len(s) {
+			i++
+			switch s[i] {
+			case 'n':
+				out.WriteByte('\n')
+			case 'r':
+				out.WriteByte('\r')
+			case 't':
+				out.WriteByte('\t')
+			case '0':
+				out.WriteByte(0)
+			case 'Z':
+				out.WriteByte(26)
+			default:
+				out.WriteByte(s[i])
+			}
+		} else {
+			out.WriteByte(s[i])
+		}
+	}
+	return out.String()
+}

pkg/readers/mysql/reader_test.go

@@ -3,12 +3,13 @@ package mysql
 import (
 	"testing"
 
+	"git.warky.dev/wdevs/relspecgo/pkg/models"
 	"git.warky.dev/wdevs/relspecgo/pkg/readers"
 )
 
 func TestReaderMapDataType(t *testing.T) {
 	r := NewReader(&readers.ReaderOptions{})
-	for _, tc := range []struct{ input, want string }{{"varchar(64)", "string"}, {"bigint unsigned", "int64"}, {"datetime", "timestamp"}, {"json", "json"}} {
+	for _, tc := range []struct{ input, want string }{{"varchar(64)", "string"}, {"bigint unsigned", "uint64"}, {"datetime", "timestamp"}, {"json", "json"}} {
 		if got := r.mapDataType(tc.input); got != tc.want {
 			t.Errorf("mapDataType(%q) = %q, want %q", tc.input, got, tc.want)
 		}
@@ -20,3 +21,17 @@ func TestReaderRequiresConnectionString(t *testing.T) {
 		t.Fatal("expected missing connection string error")
 	}
 }
+
+func TestRelationshipNamesCannotCollapseDistinctForeignKeys(t *testing.T) {
+	table := models.InitTable("t", "app")
+	reader := NewReader(&readers.ReaderOptions{})
+	for _, c := range []*models.Constraint{
+		{Name: "a_to_b", ReferencedTable: "c"},
+		{Name: "a", ReferencedTable: "b_to_c"},
+	} {
+		reader.deriveRelationship(table, c)
+	}
+	if len(table.Relationships) != 2 {
+		t.Fatalf("distinct foreign keys collapsed: %+v", table.Relationships)
+	}
+}

pkg/writers/mysql/conversion_test.go

@@ -0,0 +1,145 @@
+package mysql
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.warky.dev/wdevs/relspecgo/pkg/models"
+	"git.warky.dev/wdevs/relspecgo/pkg/transform"
+	"git.warky.dev/wdevs/relspecgo/pkg/writers"
+)
+
+func TestStrictConversionPreflightsAllObjects(t *testing.T) {
+	db := shopDB()
+	unsupported := models.InitTable("unsupported", "shop")
+	col := models.InitColumn("opaque", "unsupported", "shop")
+	col.Type = "unknown_type"
+	unsupported.Columns[col.Name] = col
+	index := models.InitIndex("partial", "unsupported", "shop")
+	index.Columns = []string{col.Name}
+	index.Where = "opaque IS NOT NULL"
+	index.Include = []string{"other"}
+	unsupported.Indexes[index.Name] = index
+	db.Schemas[0].Tables = append(db.Schemas[0].Tables, unsupported)
+	out := filepath.Join(t.TempDir(), "existing.sql")
+	if err := os.WriteFile(out, []byte("keep existing contents"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	opts := &writers.WriterOptions{StrictConversion: true, OutputPath: out}
+	err := NewWriter(opts).WriteDatabase(db)
+	for _, want := range []string{"lossy MySQL conversion rejected", "unknown type", "partial predicate", "INCLUDE"} {
+		if err == nil || !strings.Contains(err.Error(), want) {
+			t.Fatalf("expected %s: %v", want, err)
+		}
+	}
+	bytes, err := os.ReadFile(out)
+	if err != nil || string(bytes) != "keep existing contents" {
+		t.Fatalf("destination changed: %q %v", bytes, err)
+	}
+	opts.Metadata = map[string]any{"connection_string": "invalid DSN"}
+	if err := NewWriter(opts).WriteDatabase(db); err == nil || !strings.Contains(err.Error(), "lossy MySQL") {
+		t.Fatalf("connected before strict validation: %v", err)
+	}
+	opts.StrictConversion = false
+	opts.Metadata = nil
+	var warnings []string
+	opts.Warning = func(s string) { warnings = append(warnings, s) }
+	if err := NewWriter(opts).WriteDatabase(db); err != nil {
+		t.Fatal(err)
+	}
+	if len(warnings) != 3 {
+		t.Fatalf("warnings: %v", warnings)
+	}
+}
+
+func TestUnsupportedModelFeaturesDiagnosed(t *testing.T) {
+	db := shopDB()
+	s := db.Schemas[0]
+	table := s.Tables[0]
+	s.Metadata["mysql_unsupported"] = []any{"trigger shop.audit", "partitioned table shop.archive"}
+	c := table.Columns["id"]
+	c.Type = "timestamptz"
+	c.Identity = true
+	c.Metadata["mysql_srs_id"] = 4326
+	check := models.InitConstraint("deferred", models.CheckConstraint)
+	check.Expression = "id > 0"
+	yes := true
+	check.Deferrable = &yes
+	table.Constraints[check.Name] = check
+	i := models.InitIndex("gin", "users", "shop")
+	i.Type = "gin"
+	i.Columns = []string{"id"}
+	table.Indexes[i.Name] = i
+	_, err := NewWriter(&writers.WriterOptions{StrictConversion: true}).Statements(db)
+	for _, want := range []string{"trigger shop.audit", "partitioned table", "time zone", "identity", "mysql_srs_id", "deferrable", "unsupported index type gin"} {
+		if err == nil || !strings.Contains(err.Error(), want) {
+			t.Errorf("missing diagnostic %q: %v", want, err)
+		}
+	}
+}
+
+func TestCanonicalDimensionsAndNativeEdit(t *testing.T) {
+	db := shopDB()
+	c := db.Schemas[0].Tables[0].Columns["age"]
+	c.Type = "decimal"
+	c.Precision = 12
+	c.Scale = 4
+	if got := columnType(c); got != "DECIMAL(12,4)" {
+		t.Fatal(got)
+	}
+	c.Type = "uint64"
+	c.Precision = 0
+	c.Scale = 0
+	if got := columnType(c); got != "BIGINT UNSIGNED" {
+		t.Fatal(got)
+	}
+	c.Metadata["mysql_type"] = "bigint unsigned"
+	c.Metadata["mysql_type_signature"] = signature(c)
+	c.Type = "int64"
+	_, err := NewWriter(&writers.WriterOptions{StrictConversion: true}).Statements(db)
+	if err == nil || !strings.Contains(err.Error(), "override native declaration") {
+		t.Fatalf("native metadata silently overrode edit: %v", err)
+	}
+	if got := columnType(c); got != "BIGINT" {
+		t.Fatal(got)
+	}
+}
+
+func TestLowercaseIndexPartsPreserveSQL(t *testing.T) {
+	db := shopDB()
+	table := db.Schemas[0].Tables[0]
+	c := models.InitColumn("Mixed", "users", "shop")
+	c.Type = "string"
+	table.Columns[c.Name] = c
+	i := models.InitIndex("MixedIndex", "users", "shop")
+	i.KeyParts = []models.IndexPart{{Name: "Mixed", Length: 8, Descending: true}, {Expression: "lower(`Mixed`)"}}
+	table.Indexes[i.Name] = i
+	model, err := transform.LowercaseIdentifiers(db)
+	if err != nil {
+		t.Fatal(err)
+	}
+	parts := model.Schemas[0].Tables[0].Indexes["mixedindex"].KeyParts
+	if parts[0].Name != "mixed" || parts[1].Expression != "lower(`Mixed`)" || i.KeyParts[0].Name != "Mixed" {
+		t.Fatalf("lowercase parts: %+v", parts)
+	}
+}
+
+func TestLowercasePrimaryIndexIsNotDuplicated(t *testing.T) {
+	db := shopDB()
+	table := db.Schemas[0].Tables[0]
+	i := models.InitIndex("PRIMARY", table.Name, table.Schema)
+	i.Unique = true
+	i.Type = "btree"
+	i.Columns = []string{"id"}
+	i.KeyParts = []models.IndexPart{{Name: "id", Descending: true}}
+	table.Indexes[i.Name] = i
+	statements, err := NewWriter(&writers.WriterOptions{StrictConversion: true, LowercaseIdentifiers: true}).Statements(db)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(statements[0], "PRIMARY KEY (`id` DESC)") || strings.Contains(statements[0], "KEY `primary`") {
+		t.Fatalf("primary key duplicated or attributes lost: %s", statements[0])
+	}
+}

pkg/writers/mysql/diagnostics.go

@@ -0,0 +1,184 @@
+package mysql
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"git.warky.dev/wdevs/relspecgo/pkg/mariadb"
+	"git.warky.dev/wdevs/relspecgo/pkg/models"
+)
+
+// Diagnostics cover modeled schema semantics and features discovered by the
+// MySQL reader. They do not certify arbitrary SQL expressions or catalog grants.
+func conversionDiagnostics(db *models.Database) []string {
+	var out []string
+	warn := func(path, feature string) { out = append(out, path+": "+feature) }
+	unsupported := func(m map[string]any) {
+		switch values := m["mysql_unsupported"].(type) {
+		case []string:
+			for _, v := range values {
+				warn(v, "unsupported object")
+			}
+		case []any:
+			for _, v := range values {
+				warn(fmt.Sprint(v), "unsupported object")
+			}
+		}
+	}
+	metadata := func(path string, m map[string]any, allowed string) {
+		if len(models.GetDirectives(m)) > 0 {
+			warn(path, "dialect directives are not emitted")
+		}
+		for _, key := range keys(m) {
+			if strings.HasPrefix(key, "mysql_") && !strings.Contains(" "+allowed+" ", " "+key+" ") {
+				warn(path, "unsupported metadata "+key+": "+fmt.Sprint(m[key]))
+			}
+		}
+	}
+	metadata("database", db.Metadata, "mysql_unsupported mysql_sql_mode")
+	modeWarning := func(path string, m map[string]any) {
+		if mode := unsupportedMode(metaString(m, "mysql_sql_mode")); mode != "" {
+			warn(path, "unsupported source SQL mode "+mode+"; generated SQL requires standard quotes and backslash escaping")
+		}
+	}
+	modeWarning("database", db.Metadata)
+	unsupported(db.Metadata)
+	if len(db.Domains) > 0 {
+		warn("database", "domains are not emitted")
+	}
+	for _, s := range db.Schemas {
+		path := s.Name
+		metadata(path, s.Metadata, "mysql_unsupported mysql_sql_mode")
+		modeWarning(path, s.Metadata)
+		unsupported(s.Metadata)
+		if len(s.Views) > 0 {
+			warn(path, "views are not emitted")
+		}
+		if len(s.Sequences) > 0 {
+			warn(path, "standalone sequences are not emitted")
+		}
+		if len(s.Enums) > 0 {
+			warn(path, "standalone enum types are not emitted; use native column enum types")
+		}
+		if len(s.Scripts) > 0 {
+			warn(path, "scripts are not emitted")
+		}
+		if s.Owner != "" || len(s.Permissions) > 0 {
+			warn(path, "ownership and permissions are not emitted")
+		}
+		for _, t := range s.Tables {
+			tp := path + "." + t.Name
+			modeWarning(tp, t.Metadata)
+			if t.Tablespace != "" {
+				warn(tp, "tablespace is not emitted")
+			}
+			metadata(tp, t.Metadata, "mysql_engine mysql_collation mysql_create_options mysql_auto_increment mysql_sql_mode")
+			if options := metaString(t.Metadata, "mysql_create_options"); options != "" {
+				warn(tp, "table CREATE_OPTIONS are not emitted: "+options)
+			}
+			for _, name := range keys(t.Columns) {
+				c := t.Columns[name]
+				cp := tp + "." + c.Name
+				metadata(cp, c.Metadata, "mysql_type mysql_type_signature mysql_charset mysql_datetime_precision mysql_default_expression mysql_default_sql mysql_default_value mysql_generation_storage mysql_invisible mysql_on_update")
+				if _, known := mariadb.CanonicalToMariaDBTypes[strings.ToLower(c.Type)]; !known && metaString(c.Metadata, "mysql_type") == "" {
+					warn(cp, "unknown type "+c.Type+" maps to "+columnType(c))
+				}
+				if native := metaString(c.Metadata, "mysql_type"); native != "" && metaString(c.Metadata, "mysql_type_signature") != signature(c) {
+					warn(cp, "edited canonical type/dimensions override native declaration "+native)
+				}
+				if c.Type == "timestamptz" {
+					warn(cp, "time zone semantics are not supported")
+				}
+				if c.Type == "jsonb" {
+					warn(cp, "jsonb storage semantics become JSON")
+				}
+				if c.Identity {
+					warn(cp, "identity semantics are not emitted; use auto_increment")
+				}
+				if c.Generated && c.GenerationExpression == "" {
+					warn(cp, "generated column has no expression")
+				}
+				if !c.Generated && c.GenerationExpression != "" {
+					warn(cp, "generation expression requires generated=true")
+				}
+				if c.Generated && (c.Default != nil || c.AutoIncrement) {
+					warn(cp, "generated column cannot preserve a default or auto_increment")
+				}
+				if storage := metaString(c.Metadata, "mysql_generation_storage"); storage != "" && storage != "STORED" && storage != "VIRTUAL" {
+					warn(cp, "unsupported generation storage "+storage)
+				}
+			}
+			for _, name := range keys(t.Constraints) {
+				c := t.Constraints[name]
+				cp := tp + " constraint " + c.Name
+				metadata(cp, c.Metadata, "mysql_enforced")
+				if c.Deferrable != nil && *c.Deferrable || c.InitiallyDeferred != nil && *c.InitiallyDeferred {
+					warn(cp, "deferrable constraints are not supported")
+				}
+				switch c.Type {
+				case models.PrimaryKeyConstraint, models.UniqueConstraint:
+				case models.CheckConstraint:
+					if c.Expression == "" {
+						warn(cp, "check constraint has no expression")
+					}
+				case models.ForeignKeyConstraint:
+					engine := metaString(t.Metadata, "mysql_engine")
+					if engine != "" && !strings.EqualFold(engine, "InnoDB") && !strings.EqualFold(engine, "NDB") {
+						warn(cp, "foreign keys are not supported by engine "+engine)
+					}
+					for _, action := range []string{c.OnDelete, c.OnUpdate} {
+						switch strings.ToUpper(action) {
+						case "", "CASCADE", "SET NULL", "RESTRICT", "NO ACTION":
+						default:
+							warn(cp, "unsupported referential action is not emitted: "+action)
+						}
+					}
+				default:
+					warn(cp, "unsupported constraint type "+string(c.Type))
+				}
+			}
+			for _, name := range keys(t.Indexes) {
+				i := t.Indexes[name]
+				ip := tp + " index " + i.Name
+				metadata(ip, i.Metadata, "mysql_visible")
+				if i.Where != "" {
+					warn(ip, "partial predicate is not emitted")
+				}
+				if len(i.Include) > 0 {
+					warn(ip, "INCLUDE columns are not emitted")
+				}
+				if i.Concurrent {
+					warn(ip, "concurrent creation is not supported")
+				}
+				if strings.EqualFold(i.Type, "hash") && !strings.EqualFold(metaString(t.Metadata, "mysql_engine"), "MEMORY") {
+					warn(ip, "HASH index requires a compatible engine; InnoDB converts it to BTREE")
+				}
+				switch strings.ToUpper(i.Type) {
+				case "", "BTREE", "HASH", "FULLTEXT", "SPATIAL":
+				default:
+					warn(ip, "unsupported index type "+i.Type+"; index is not emitted")
+				}
+				for _, p := range i.KeyParts {
+					if (p.Name == "") == (p.Expression == "") {
+						warn(ip, "key part requires exactly one name or expression")
+					}
+				}
+			}
+			for _, name := range keys(t.Relationships) {
+				r := t.Relationships[name]
+				if t.Constraints[r.ForeignKey] == nil {
+					warn(tp+" relationship "+r.Name, "no backing foreign key constraint; relationship is not emitted")
+				}
+			}
+		}
+	}
+	sort.Strings(out)
+	unique := out[:0]
+	for _, d := range out {
+		if len(unique) == 0 || unique[len(unique)-1] != d {
+			unique = append(unique, d)
+		}
+	}
+	return unique
+}

pkg/writers/mysql/live_diagnostics_test.go

@@ -0,0 +1,140 @@
+package mysql_test
+
+import (
+	"database/sql"
+	"fmt"
+	"git.warky.dev/wdevs/relspecgo/pkg/models"
+	driver "github.com/go-sql-driver/mysql"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"git.warky.dev/wdevs/relspecgo/pkg/readers"
+	rmysql "git.warky.dev/wdevs/relspecgo/pkg/readers/mysql"
+	"git.warky.dev/wdevs/relspecgo/pkg/writers"
+	wmysql "git.warky.dev/wdevs/relspecgo/pkg/writers/mysql"
+)
+
+func TestLiveUnsupportedObjectsDiagnosed(t *testing.T) {
+	conn := os.Getenv("RELSPEC_TEST_MYSQL_CONN")
+	if conn == "" {
+		t.Skip("RELSPEC_TEST_MYSQL_CONN is not set")
+	}
+	db, err := sql.Open("mysql", conn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { db.Close() })
+	prefix := fmt.Sprintf("unsupported_%d", time.Now().UnixNano())
+	table, view, trigger := prefix+"_table", prefix+"_view", prefix+"_trigger"
+	t.Cleanup(func() {
+		for _, stmt := range []string{"DROP VIEW IF EXISTS " + view, "DROP TRIGGER IF EXISTS " + trigger, "DROP TABLE IF EXISTS " + table} {
+			if _, err := db.Exec(stmt); err != nil {
+				t.Error(err)
+			}
+		}
+	})
+	for _, stmt := range []string{
+		"CREATE TABLE " + table + " (id INT PRIMARY KEY) PARTITION BY HASH(id) PARTITIONS 2",
+		"CREATE VIEW " + view + " AS SELECT id FROM " + table,
+		"CREATE TRIGGER " + trigger + " BEFORE INSERT ON " + table + " FOR EACH ROW SET NEW.id = NEW.id + 1",
+	} {
+		if _, err := db.Exec(stmt); err != nil {
+			t.Fatalf("%s: %v", stmt, err)
+		}
+	}
+	model, err := rmysql.NewReader(&readers.ReaderOptions{ConnectionString: conn}).ReadDatabase()
+	if err != nil {
+		t.Fatal(err)
+	}
+	path := filepath.Join(t.TempDir(), "schema.sql")
+	if err := os.WriteFile(path, []byte("original"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	err = wmysql.NewWriter(&writers.WriterOptions{StrictConversion: true, OutputPath: path}).WriteDatabase(model)
+	for _, want := range []string{"partitioned table", view, trigger} {
+		if err == nil || !strings.Contains(err.Error(), want) {
+			t.Errorf("missing diagnostic %s: %v", want, err)
+		}
+	}
+	bytes, readErr := os.ReadFile(path)
+	if readErr != nil || string(bytes) != "original" {
+		t.Fatalf("strict failure touched file: %s %v", bytes, readErr)
+	}
+	// Schema-filtered/library writes retain discovery diagnostics as well.
+	err = wmysql.NewWriter(&writers.WriterOptions{StrictConversion: true}).WriteSchema(model.Schemas[0])
+	if err == nil || !strings.Contains(err.Error(), trigger) {
+		t.Fatalf("filtered schema lost diagnostics: %v", err)
+	}
+	var warnings []string
+	_, err = wmysql.NewWriter(&writers.WriterOptions{Warning: func(s string) { warnings = append(warnings, s) }}).Statements(model)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, want := range []string{view, trigger, table} {
+		found := false
+		for _, warning := range warnings {
+			if strings.Contains(warning, want) {
+				found = true
+			}
+		}
+		if !found {
+			t.Errorf("no warning for %s: %v", want, warnings)
+		}
+	}
+}
+
+func TestLiveUnsupportedSQLModeFailsBeforeDDL(t *testing.T) {
+	conn := os.Getenv("RELSPEC_TEST_MYSQL_CONN")
+	if conn == "" {
+		t.Skip("RELSPEC_TEST_MYSQL_CONN is not set")
+	}
+	for _, mode := range []string{"NO_BACKSLASH_ESCAPES", "ANSI_QUOTES"} {
+		t.Run(mode, func(t *testing.T) {
+			cfg, err := driver.ParseDSN(conn)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if cfg.Params == nil {
+				cfg.Params = map[string]string{}
+			}
+			cfg.Params["sql_mode"] = "'" + mode + "'"
+			modeConn := cfg.FormatDSN()
+			model, err := rmysql.NewReader(&readers.ReaderOptions{ConnectionString: modeConn}).ReadDatabase()
+			if err != nil {
+				t.Fatal(err)
+			}
+			if _, err := wmysql.NewWriter(&writers.WriterOptions{StrictConversion: true}).Statements(model); err == nil || !strings.Contains(err.Error(), mode) {
+				t.Fatalf("source mode not diagnosed: %v", err)
+			}
+			db, err := sql.Open("mysql", conn)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer db.Close()
+			name := fmt.Sprintf("mode_%d", time.Now().UnixNano())
+			defer db.Exec("DROP TABLE IF EXISTS " + name)
+			target := models.InitDatabase(cfg.DBName)
+			s := models.InitSchema(cfg.DBName)
+			target.Schemas = append(target.Schemas, s)
+			table := models.InitTable(name, s.Name)
+			s.Tables = append(s.Tables, table)
+			c := models.InitColumn("id", name, s.Name)
+			c.Type = "int"
+			table.Columns[c.Name] = c
+			err = wmysql.NewWriter(&writers.WriterOptions{StrictConversion: true, Metadata: map[string]any{"connection_string": modeConn}}).WriteDatabase(target)
+			if err == nil || !strings.Contains(err.Error(), mode) {
+				t.Fatalf("target mode not rejected: %v", err)
+			}
+			var count int
+			if err := db.QueryRow("SELECT COUNT(*) FROM information_schema.TABLES WHERE TABLE_SCHEMA=? AND TABLE_NAME=?", cfg.DBName, name).Scan(&count); err != nil {
+				t.Fatal(err)
+			}
+			if count != 0 {
+				t.Fatal("mode rejection occurred after DDL")
+			}
+		})
+	}
+}

pkg/writers/mysql/live_roundtrip_test.go

@@ -0,0 +1,242 @@
+package mysql_test
+
+import (
+	"database/sql"
+	"encoding/json"
+	"fmt"
+	"gopkg.in/yaml.v3"
+	"os"
+	"reflect"
+	"sort"
+	"strings"
+	"testing"
+	"time"
+
+	"git.warky.dev/wdevs/relspecgo/pkg/models"
+	"git.warky.dev/wdevs/relspecgo/pkg/readers"
+	rmysql "git.warky.dev/wdevs/relspecgo/pkg/readers/mysql"
+	"git.warky.dev/wdevs/relspecgo/pkg/writers"
+	wmysql "git.warky.dev/wdevs/relspecgo/pkg/writers/mysql"
+	driver "github.com/go-sql-driver/mysql"
+)
+
+func TestLiveSchemaRoundTrip(t *testing.T) {
+	conn := os.Getenv("RELSPEC_TEST_MYSQL_CONN")
+	if conn == "" {
+		t.Skip("RELSPEC_TEST_MYSQL_CONN is not set")
+	}
+	db, err := sql.Open("mysql", conn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { db.Close() })
+	prefix := fmt.Sprintf("rt_%d", time.Now().UnixNano())
+	parent, child := prefix+"_zparent", prefix+"_achild"
+	q := func(n string) string { return "`" + strings.ReplaceAll(n, "`", "``") + "`" }
+	exec := func(stmt string) {
+		t.Helper()
+		if _, err := db.Exec(stmt); err != nil {
+			t.Fatalf("%v\n%s", err, stmt)
+		}
+	}
+	t.Cleanup(func() {
+		for _, name := range []string{child + "_copy", child, parent + "_copy", parent} {
+			if _, err := db.Exec("DROP TABLE IF EXISTS " + q(name)); err != nil {
+				t.Errorf("cleanup %s: %v", name, err)
+			}
+		}
+	})
+	exec("CREATE TABLE " + q(parent) + ` (
+ id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
+ code CHAR(3) NOT NULL,
+ email VARCHAR(100) NOT NULL,
+ label VARCHAR(64) DEFAULT 'don''t (change)' COMMENT 'column''s comment',
+ amount DECIMAL(12,4) NOT NULL DEFAULT 3.2500,
+ medium MEDIUMINT UNSIGNED,
+ flags BIT(8) DEFAULT b'00001010',
+ status ENUM('one','two','don''t, split') DEFAULT 'don''t, split',
+ choices SET('a','b') DEFAULT 'a,b',
+ stamp TIMESTAMP(6) NULL DEFAULT CURRENT_TIMESTAMP(6) ON UPDATE CURRENT_TIMESTAMP(6),
+ duration TIME(4),
+ bytes VARBINARY(16),
+ binary_def VARBINARY(8) DEFAULT X'00275CFF',
+ slash VARCHAR(64) DEFAULT 'C:\\temp\\file',
+ uuid_value CHAR(36) DEFAULT (uuid()),
+ hidden_col INT INVISIBLE,
+ dt DATETIME(6) DEFAULT '2020-01-02 03:04:05.123456',
+ payload MEDIUMBLOB,
+ doc TEXT DEFAULT ('first;
+-- data, not a comment
+last'),
+ generated_amount DECIMAL(13,4) GENERATED ALWAYS AS (amount * 2) STORED,
+ virtual_label VARCHAR(80) GENERATED ALWAYS AS (concat('prefix:',lower(label))) VIRTUAL,
+ PRIMARY KEY (id,code),
+ UNIQUE KEY email_unique (email),
+ UNIQUE KEY pair_unique (label,email),
+ UNIQUE KEY unique_expression ((concat(lower(code),'-x')),email),
+ KEY prefix_desc (label(10) DESC),
+ KEY expression_key ((lower(email))),
+ KEY invisible_key (medium) INVISIBLE COMMENT 'index''s comment',
+ FULLTEXT KEY text_search (doc),
+ CONSTRAINT ` + q(prefix+"_amount_check") + ` CHECK (amount >= 0),
+ CONSTRAINT ` + q(prefix+"_optional_check") + ` CHECK (medium > 0 AND status <> 'forbidden;-- value') NOT ENFORCED
+ ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci COMMENT='table''s comment'`)
+	exec("CREATE TABLE " + q(child) + ` (
+ id INT PRIMARY KEY,
+ parent_id BIGINT UNSIGNED,
+ parent_code CHAR(3),
+ parent_email VARCHAR(100),
+ CONSTRAINT ` + q(prefix+"_composite_fk") + ` FOREIGN KEY (parent_id,parent_code) REFERENCES ` + q(parent) + ` (id,code) ON DELETE SET NULL ON UPDATE CASCADE,
+ CONSTRAINT ` + q(prefix+"_email_fk") + ` FOREIGN KEY (parent_email) REFERENCES ` + q(parent) + ` (email) ON DELETE CASCADE ON UPDATE RESTRICT
+ ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci`)
+	readerConfig, err := driver.ParseDSN(conn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if readerConfig.Params == nil {
+		readerConfig.Params = map[string]string{}
+	}
+	readerConfig.Params["sql_quote_show_create"] = "0" // reader must ensure quoted native metadata
+	read := func() *models.Database {
+		t.Helper()
+		model, err := rmysql.NewReader(&readers.ReaderOptions{ConnectionString: readerConfig.FormatDSN()}).ReadDatabase()
+		if err != nil {
+			t.Fatal(err)
+		}
+		return model
+	}
+	model := read()
+	var selected []*models.Table
+	for _, table := range model.Schemas[0].Tables {
+		if table.Name == parent || table.Name == child {
+			selected = append(selected, table)
+		}
+	}
+	if len(selected) != 2 {
+		t.Fatalf("read %d fixture tables", len(selected))
+	}
+	model.Schemas[0].Tables = selected
+	model.Metadata = nil
+	model.Schemas[0].Metadata = nil // unrelated pre-existing test objects are outside this fixture
+	for _, table := range selected {
+		if table.Name == parent {
+			if table.Columns["id"].Type != "uint64" {
+				t.Fatal("unsigned type lost")
+			}
+			if table.Columns["amount"].Precision != 12 || table.Columns["amount"].Scale != 4 {
+				t.Fatal("decimal dimensions lost")
+			}
+			if table.Indexes["expression_key"].KeyParts[0].Expression == "" {
+				t.Fatal("functional index expression lost")
+			}
+		} else if len(table.Relationships) != 2 {
+			t.Fatalf("foreign key relationships collapsed: %d", len(table.Relationships))
+		}
+	}
+	// Exercise the serialized model boundary as well as the native reader objects.
+	encoded, err := json.Marshal(model)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var target models.Database
+	if err := json.Unmarshal(encoded, &target); err != nil {
+		t.Fatal(err)
+	}
+	yamlModel, err := yaml.Marshal(&target)
+	if err != nil {
+		t.Fatal(err)
+	}
+	target = models.Database{}
+	if err := yaml.Unmarshal(yamlModel, &target); err != nil {
+		t.Fatal(err)
+	}
+	for _, table := range target.Schemas[0].Tables {
+		table.Name += "_copy"
+		for _, col := range table.Columns {
+			col.Table = table.Name
+		}
+		for _, index := range table.Indexes {
+			index.Table = table.Name
+		}
+		constraints := map[string]*models.Constraint{}
+		for _, c := range table.Constraints {
+			c.Table = table.Name
+			if c.Type == models.ForeignKeyConstraint {
+				c.ReferencedTable += "_copy"
+			}
+			if c.Type == models.ForeignKeyConstraint || c.Type == models.CheckConstraint {
+				c.Name += "_copy"
+			}
+			constraints[c.Name] = c
+		}
+		table.Constraints = constraints
+		for _, r := range table.Relationships {
+			r.FromTable += "_copy"
+			r.ToTable += "_copy"
+			r.ForeignKey += "_copy"
+		}
+	}
+	opts := &writers.WriterOptions{StrictConversion: true, Metadata: map[string]any{"connection_string": conn}}
+	if err := wmysql.NewWriter(opts).WriteDatabase(&target); err != nil {
+		t.Fatal(err)
+	}
+	show := func(table string) string {
+		t.Helper()
+		var name, ddl string
+		if err := db.QueryRow("SHOW CREATE TABLE "+q(table)).Scan(&name, &ddl); err != nil {
+			t.Fatal(err)
+		}
+		ddl = strings.ReplaceAll(ddl, "_copy", "")
+		// Index creation order is not semantic. Keep column and constraint order intact.
+		lines := strings.Split(ddl, "\n")
+		var indexes []string
+		for _, line := range lines {
+			if strings.HasPrefix(strings.TrimSpace(line), "KEY ") {
+				indexes = append(indexes, line)
+			}
+		}
+		sort.Strings(indexes)
+		n := 0
+		for i, line := range lines {
+			if strings.HasPrefix(strings.TrimSpace(line), "KEY ") {
+				lines[i] = indexes[n]
+				n++
+			}
+		}
+		return strings.Join(lines, "\n")
+	}
+	for _, name := range []string{parent, child} {
+		a, b := show(name), show(name+"_copy")
+		if a != b {
+			t.Errorf("schema mismatch\nsource:\n%s\ntarget:\n%s", a, b)
+		}
+	}
+	again := read()
+	for _, table := range again.Schemas[0].Tables {
+		if table.Name == parent+"_copy" && !reflect.DeepEqual(table.Columns["amount"].Metadata, selected[1].Columns["amount"].Metadata) {
+			t.Error("type metadata changed on second read")
+		}
+	}
+	// Verify constraints and defaults as behavior, after comparing untouched schemas.
+	exec("INSERT INTO " + q(parent+"_copy") + " (id,code,email) VALUES (18446744073709551614,'abc','one@example.com')")
+	exec("INSERT INTO " + q(child+"_copy") + " (id,parent_id,parent_code,parent_email) VALUES (1,18446744073709551614,'abc','one@example.com')")
+	if _, err := db.Exec("INSERT INTO " + q(child+"_copy") + " (id,parent_id,parent_code) VALUES (2,123,'abc')"); err == nil {
+		t.Error("foreign key is not enforced")
+	}
+	if _, err := db.Exec("UPDATE " + q(parent+"_copy") + " SET amount=-1"); err == nil {
+		t.Error("check is not enforced")
+	}
+	var label, doc, binaryHex, slash string
+	var flags int
+	if err := db.QueryRow("SELECT label,doc,flags+0,HEX(binary_def),slash FROM "+q(parent+"_copy")).Scan(&label, &doc, &flags, &binaryHex, &slash); err != nil {
+		t.Fatal(err)
+	}
+	for _, table := range read().Schemas[0].Tables {
+		if table.Name == parent+"_copy" && table.Metadata["mysql_auto_increment"] != "18446744073709551615" {
+			t.Errorf("large auto-increment counter lost: %v", table.Metadata["mysql_auto_increment"])
+		}
+	}
+	if label != "don't (change)" || doc != "first;\n-- data, not a comment\nlast" || flags != 10 || binaryHex != "00275CFF" || slash != `C:\temp\file` {
+		t.Errorf("defaults corrupted: %q %q %d %s %q", label, doc, flags, binaryHex, slash)
+	}
+}

pkg/writers/mysql/writer.go

@@ -7,13 +7,14 @@ import (
 	"io"
 	"os"
 	"sort"
+	"strconv"
 	"strings"
 
-	_ "github.com/go-sql-driver/mysql"
-
 	"git.warky.dev/wdevs/relspecgo/pkg/mariadb"
 	"git.warky.dev/wdevs/relspecgo/pkg/models"
+	"git.warky.dev/wdevs/relspecgo/pkg/transform"
 	"git.warky.dev/wdevs/relspecgo/pkg/writers"
+	_ "github.com/go-sql-driver/mysql"
 )
 
 type Writer struct {
@@ -22,88 +23,192 @@ type Writer struct {
 }
 
 func NewWriter(options *writers.WriterOptions) *Writer { return &Writer{options: options} }
-func (w *Writer) WriteDatabase(db *models.Database) error {
+
+// Statements preflights the whole model, emits conversion diagnostics, and returns
+// executable units. No output files or database connections are opened here.
+func (w *Writer) Statements(db *models.Database) ([]string, error) {
 	if w.options == nil {
-		return fmt.Errorf("writer options are required")
+		return nil, fmt.Errorf("writer options are required")
 	}
-	if conn, ok := w.options.Metadata["connection_string"].(string); ok && conn != "" {
+	if db == nil {
-		return w.execute(db, conn)
+		return nil, fmt.Errorf("database is required")
 	}
-	release, err := w.openOutput()
+	if w.options.LowercaseIdentifiers {
-	if err != nil {
+		var err error
-		return err
+		db, err = transform.LowercaseIdentifiers(db)
-	}
-	defer release()
-	return w.writeDatabaseDDL(db)
-}
-
-func (w *Writer) writeDatabaseDDL(db *models.Database) error {
-	if _, err := fmt.Fprintf(w.writer, "-- MySQL Database Schema\n-- Database: %s\n-- Generated by RelSpec\n\n", db.Name); err != nil {
-		return err
-	}
-	for _, s := range db.Schemas {
-		if err := w.WriteSchema(s); err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
-// openOutput points w.writer at the configured destination (output file or
-// stdout) when none is set, and returns a func that releases it again.
-func (w *Writer) openOutput() (func(), error) {
-	if w.writer != nil {
-		return func() {}, nil
-	}
-	if w.options != nil && w.options.OutputPath != "" {
-		f, err := os.Create(w.options.OutputPath)
 		if err != nil {
 			return nil, err
 		}
-		w.writer = f
-		return func() {
-			f.Close()
-			w.writer = nil
-		}, nil
 	}
-	w.writer = os.Stdout
+	diagnostics := conversionDiagnostics(db)
-	return func() { w.writer = nil }, nil
+	if len(diagnostics) > 0 && w.options.StrictConversion {
+		return nil, fmt.Errorf("lossy MySQL conversion rejected:\n- %s", strings.Join(diagnostics, "\n- "))
 	}
-
+	for _, d := range diagnostics {
-func (w *Writer) WriteSchema(s *models.Schema) error {
+		if w.options.Warning != nil {
-	release, err := w.openOutput()
+			w.options.Warning(d)
+		} else {
+			fmt.Fprintln(os.Stderr, "warning: MySQL conversion: "+d)
+		}
+	}
+	return databaseStatements(db), nil
+}
+func (w *Writer) WriteDatabase(db *models.Database) error {
+	statements, err := w.Statements(db)
 	if err != nil {
 		return err
 	}
-	defer release()
+	if conn, ok := w.options.Metadata["connection_string"].(string); ok && conn != "" {
-	for _, t := range s.Tables {
+		return w.execute(statements, conn)
-		if err := w.writeTable(s, t); err != nil {
+	}
+	if w.writer != nil {
+		return writeStatements(w.writer, statements, db.Name)
+	}
+	if w.options.OutputPath == "" {
+		return writeStatements(os.Stdout, statements, db.Name)
+	}
+	f, err := os.Create(w.options.OutputPath)
+	if err != nil {
+		return err
+	}
+	err = writeStatements(f, statements, db.Name)
+	closeErr := f.Close()
+	if err != nil {
+		return err
+	}
+	return closeErr
+}
+func writeStatements(out io.Writer, statements []string, name string) error {
+	name = strings.NewReplacer("\n", " ", "\r", " ").Replace(name)
+	if _, err := fmt.Fprintf(out, "-- Database: %s\n", name); err != nil {
+		return err
+	}
+	if _, err := io.WriteString(out, "-- MySQL table schema; generated by RelSpec\n\n"); err != nil {
+		return err
+	}
+	for _, stmt := range statements {
+		if _, err := io.WriteString(out, stmt); err != nil {
 			return err
 		}
 	}
 	return nil
 }
-
+func (w *Writer) WriteSchema(s *models.Schema) error {
+	return w.WriteDatabase(&models.Database{Schemas: []*models.Schema{s}})
+}
 func (w *Writer) WriteTable(t *models.Table) error {
-	release, err := w.openOutput()
+	return w.WriteSchema(&models.Schema{Name: "", Tables: []*models.Table{t}})
-	if err != nil {
-		return err
-	}
-	defer release()
-	return w.writeTable(nil, t)
 }
 
-func (w *Writer) writeTable(s *models.Schema, t *models.Table) error {
+func qualified(schema, name string) string {
-	_, err := io.WriteString(w.writer, tableStatement(s, t))
+	if schema == "" {
-	return err
+		return quote(name)
+	}
+	return quote(schema) + "." + quote(name)
+}
+func keys[T any](m map[string]T) []string {
+	out := make([]string, 0, len(m))
+	for k := range m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
+}
+func metaString(m map[string]any, key string) string { v, _ := m[key].(string); return v }
+func metaBool(m map[string]any, key string, def bool) bool {
+	v, ok := m[key].(bool)
+	if ok {
+		return v
+	}
+	return def
+}
+func signature(c *models.Column) string {
+	return fmt.Sprintf("%s/%d/%d/%d", c.Type, c.Length, c.Precision, c.Scale)
+}
+func columnType(c *models.Column) string {
+	if native := metaString(c.Metadata, "mysql_type"); native != "" && metaString(c.Metadata, "mysql_type_signature") == signature(c) {
+		return native
+	}
+	typ := mariadb.ConvertCanonicalToMariaDB(c.Type)
+	switch strings.ToLower(c.Type) {
+	case "string":
+		if c.Length > 0 {
+			typ = fmt.Sprintf("VARCHAR(%d)", c.Length)
+		}
+	case "decimal":
+		if c.Precision > 0 {
+			typ = fmt.Sprintf("DECIMAL(%d,%d)", c.Precision, c.Scale)
+		}
+	case "timestamp", "time":
+		if c.Precision > 0 {
+			typ += fmt.Sprintf("(%d)", c.Precision)
+		}
+	}
+	return typ
 }
 
+// MySQL string literals use doubled quotes and escaped backslashes. The output
+// assumes the server's standard SQL mode (NO_BACKSLASH_ESCAPES is not enabled).
+func literal(s string) string {
+	return "'" + strings.ReplaceAll(strings.ReplaceAll(s, "\\", "\\\\"), "'", "''") + "'"
+}
+func defaultSQL(c *models.Column) string {
+	value := fmt.Sprint(c.Default)
+	if native := metaString(c.Metadata, "mysql_default_sql"); native != "" && metaString(c.Metadata, "mysql_default_value") == value {
+		return native
+	}
+	if strings.HasPrefix(metaString(c.Metadata, "mysql_type"), "bit(") && strings.HasPrefix(value, "b'") && strings.HasSuffix(value, "'") && strings.Trim(value[2:len(value)-1], "01") == "" {
+		return value
+	}
+	if metaBool(c.Metadata, "mysql_default_expression", false) {
+		if strings.HasPrefix(strings.ToUpper(value), "CURRENT_TIMESTAMP") {
+			return value
+		}
+		return "(" + value + ")"
+	}
+	switch strings.ToLower(c.Type) {
+	case "text", "json", "jsonb", "bytea":
+		return "(" + literal(value) + ")"
+	case "string", "uuid", "date", "time", "timestamp", "timestamptz":
+		return literal(value)
+	case "bool", "boolean":
+		if value == "true" {
+			return "1"
+		}
+		if value == "false" {
+			return "0"
+		}
+	}
+	// Numeric defaults are values, never executable fragments.
+	if _, err := strconv.ParseFloat(value, 64); err == nil {
+		return value
+	}
+	return literal(value)
+}
+func indexParts(i *models.Index) string {
+	if len(i.KeyParts) == 0 {
+		return quoted(i.Columns)
+	}
+	parts := make([]string, 0, len(i.KeyParts))
+	for _, p := range i.KeyParts {
+		s := quote(p.Name)
+		if p.Expression != "" {
+			s = "(" + p.Expression + ")"
+		}
+		if p.Length > 0 {
+			s += fmt.Sprintf("(%d)", p.Length)
+		}
+		if p.Descending {
+			s += " DESC"
+		}
+		parts = append(parts, s)
+	}
+	return strings.Join(parts, ", ")
+}
 func tableStatement(s *models.Schema, t *models.Table) string {
-	name := t.Name
+	schema := ""
 	if s != nil {
-		name = fmt.Sprintf("%s.%s", quote(s.Name), quote(t.Name))
+		schema = s.Name
-	} else {
-		name = quote(name)
 	}
 	cols := make([]*models.Column, 0, len(t.Columns))
 	for _, c := range t.Columns {
@@ -118,76 +223,196 @@ func tableStatement(s *models.Schema, t *models.Table) string {
 	defs := []string{}
 	pk := []string{}
 	for _, c := range cols {
-		d := fmt.Sprintf("  %s %s", quote(c.Name), mariadb.ConvertCanonicalToMariaDB(c.Type))
+		d := "  " + quote(c.Name) + " " + columnType(c)
-		if c.Length > 0 && strings.EqualFold(c.Type, "string") {
+		if charset := metaString(c.Metadata, "mysql_charset"); charset != "" && c.Collation != metaString(t.Metadata, "mysql_collation") {
-			d = fmt.Sprintf("  %s VARCHAR(%d)", quote(c.Name), c.Length)
+			d += " CHARACTER SET " + quote(charset)
+		}
+		if c.Collation != "" && c.Collation != metaString(t.Metadata, "mysql_collation") {
+			d += " COLLATE " + quote(c.Collation)
+		}
+		if c.Generated {
+			d += " GENERATED ALWAYS AS (" + c.GenerationExpression + ")"
+			if strings.EqualFold(metaString(c.Metadata, "mysql_generation_storage"), "STORED") {
+				d += " STORED"
+			} else {
+				d += " VIRTUAL"
+			}
 		}
 		if c.NotNull {
 			d += " NOT NULL"
+		} else if !c.Generated {
+			d += " NULL"
 		}
 		if c.AutoIncrement {
 			d += " AUTO_INCREMENT"
 		}
-		if c.Default != nil {
+		if c.Default != nil && !c.Generated {
-			d += fmt.Sprintf(" DEFAULT %s", writers.QuoteDefaultValue(fmt.Sprint(c.Default), c.Type))
+			d += " DEFAULT " + defaultSQL(c)
+		}
+		if upd := metaString(c.Metadata, "mysql_on_update"); upd != "" {
+			d += " ON UPDATE " + upd
+		}
+		if metaBool(c.Metadata, "mysql_invisible", false) {
+			d += " INVISIBLE"
+		}
+		if c.Comment != "" {
+			d += " COMMENT " + literal(c.Comment)
 		}
 		defs = append(defs, d)
 		if c.IsPrimaryKey {
-			pk = append(pk, quote(c.Name))
+			pk = append(pk, c.Name)
 		}
 	}
-	constraintNames := make([]string, 0, len(t.Constraints))
+	for _, name := range keys(t.Constraints) {
-	for name := range t.Constraints {
-		constraintNames = append(constraintNames, name)
-	}
-	sort.Strings(constraintNames)
-	for _, name := range constraintNames {
 		c := t.Constraints[name]
 		if c.Type == models.PrimaryKeyConstraint {
-			pk = nil
+			pk = c.Columns
-			for _, n := range c.Columns {
-				pk = append(pk, quote(n))
-			}
 			break
 		}
 	}
-	if len(pk) > 0 {
+	var primaryIndex *models.Index
-		defs = append(defs, "  PRIMARY KEY ("+strings.Join(pk, ", ")+")")
+	for name, i := range t.Indexes {
+		if strings.EqualFold(name, "PRIMARY") {
+			primaryIndex = i
+			break
 		}
-	for _, name := range constraintNames {
+	}
+	if i := primaryIndex; i != nil {
+		defs = append(defs, "  PRIMARY KEY ("+indexParts(i)+")")
+	} else if len(pk) > 0 {
+		defs = append(defs, "  PRIMARY KEY ("+quoted(pk)+")")
+	}
+	for _, name := range keys(t.Constraints) {
 		c := t.Constraints[name]
-		if c.Type == models.UniqueConstraint {
+		switch c.Type {
-			defs = append(defs, fmt.Sprintf("  CONSTRAINT %s UNIQUE (%s)", quote(c.Name), quoted(c.Columns)))
+		case models.UniqueConstraint:
+			if t.Indexes[c.Name] == nil {
+				defs = append(defs, "  CONSTRAINT "+quote(c.Name)+" UNIQUE ("+quoted(c.Columns)+")")
+			}
+		case models.CheckConstraint:
+			d := "  CONSTRAINT " + quote(c.Name) + " CHECK (" + c.Expression + ")"
+			if !metaBool(c.Metadata, "mysql_enforced", true) {
+				d += " NOT ENFORCED"
+			}
+			defs = append(defs, d)
 		}
 	}
-	return fmt.Sprintf("CREATE TABLE IF NOT EXISTS %s (\n%s\n) ENGINE=InnoDB;\n\n", name, strings.Join(defs, ",\n"))
+	for _, name := range keys(t.Indexes) {
+		i := t.Indexes[name]
+		if strings.EqualFold(name, "PRIMARY") {
+			continue
+		}
+		method := strings.ToUpper(i.Type)
+		if method != "" && method != "BTREE" && method != "HASH" && method != "FULLTEXT" && method != "SPATIAL" {
+			continue
+		}
+		kind := "KEY"
+		if i.Unique {
+			kind = "UNIQUE KEY"
+		}
+		if method == "FULLTEXT" || method == "SPATIAL" {
+			kind = method + " KEY"
+		}
+		d := "  " + kind + " " + quote(i.Name) + " (" + indexParts(i) + ")"
+		if method == "HASH" {
+			d += " USING " + method
+		}
+		if !metaBool(i.Metadata, "mysql_visible", true) {
+			d += " INVISIBLE"
+		}
+		if i.Comment != "" {
+			d += " COMMENT " + literal(i.Comment)
+		}
+		defs = append(defs, d)
+	}
+	engine := metaString(t.Metadata, "mysql_engine")
+	if engine == "" {
+		engine = "InnoDB"
+	}
+	tail := " ENGINE=" + quote(engine)
+	if engine == "InnoDB" {
+		tail = " ENGINE=InnoDB"
+	}
+	if coll := metaString(t.Metadata, "mysql_collation"); coll != "" {
+		tail += " COLLATE=" + quote(coll)
+	}
+	if auto := metaString(t.Metadata, "mysql_auto_increment"); auto != "" {
+		if _, err := strconv.ParseUint(auto, 10, 64); err == nil {
+			tail += " AUTO_INCREMENT=" + auto
+		}
+	}
+	if t.Comment != "" {
+		tail += " COMMENT=" + literal(t.Comment)
+	}
+	return "CREATE TABLE IF NOT EXISTS " + qualified(schema, t.Name) + " (\n" + strings.Join(defs, ",\n") + "\n)" + tail + ";\n\n"
 }
-
 func databaseStatements(db *models.Database) []string {
 	var statements []string
-	for _, schema := range db.Schemas {
+	for _, s := range db.Schemas {
-		for _, table := range schema.Tables {
+		for _, t := range s.Tables {
-			statements = append(statements, tableStatement(schema, table))
+			statements = append(statements, tableStatement(s, t))
+		}
+	}
+	// References are added after all tables, supporting cycles and forward references.
+	for _, s := range db.Schemas {
+		for _, t := range s.Tables {
+			for _, name := range keys(t.Constraints) {
+				c := t.Constraints[name]
+				if c.Type != models.ForeignKeyConstraint {
+					continue
+				}
+				rs := c.ReferencedSchema
+				if rs == "" {
+					rs = s.Name
+				}
+				stmt := "ALTER TABLE " + qualified(s.Name, t.Name) + " ADD CONSTRAINT " + quote(c.Name) + " FOREIGN KEY (" + quoted(c.Columns) + ") REFERENCES " + qualified(rs, c.ReferencedTable) + " (" + quoted(c.ReferencedColumns) + ")"
+				if validAction(c.OnDelete) && c.OnDelete != "" {
+					stmt += " ON DELETE " + strings.ToUpper(c.OnDelete)
+				}
+				if validAction(c.OnUpdate) && c.OnUpdate != "" {
+					stmt += " ON UPDATE " + strings.ToUpper(c.OnUpdate)
+				}
+				statements = append(statements, stmt+";\n\n")
+			}
 		}
 	}
 	return statements
 }
-
+func (w *Writer) execute(statements []string, conn string) error {
-func (w *Writer) execute(dbm *models.Database, conn string) error {
+	if w.options.AtomicExecution {
-	statements := databaseStatements(dbm)
+		return fmt.Errorf("MySQL DDL implicitly commits; atomic execution is unsupported")
+	}
 	db, err := sql.Open("mysql", conn)
 	if err != nil {
 		return fmt.Errorf("failed to connect: %w", err)
 	}
 	defer db.Close()
-	for _, stmt := range statements {
+	session, err := db.Conn(context.Background())
-		if _, err := db.ExecContext(context.Background(), stmt); err != nil {
+	if err != nil {
 		return fmt.Errorf("failed to execute SQL: %w", err)
 	}
+	defer session.Close()
+	var mode string
+	if err := session.QueryRowContext(context.Background(), "SELECT @@SESSION.sql_mode").Scan(&mode); err != nil {
+		return fmt.Errorf("read MySQL SQL mode: %w", err)
+	}
+	if mode = unsupportedMode(mode); mode != "" {
+		return fmt.Errorf("MySQL execution requires standard quotes and backslash escaping; %s is enabled", mode)
+	}
+	var failures []string
+	for n, stmt := range statements {
+		if _, err := session.ExecContext(context.Background(), stmt); err != nil {
+			failures = append(failures, fmt.Sprintf("statement %d: %v", n+1, err))
+			if !w.options.ContinueOnError {
+				break
+			}
+		}
+	}
+	if len(failures) > 0 {
+		return fmt.Errorf("failed to execute SQL: %s", strings.Join(failures, "; "))
 	}
 	return nil
 }
-
 func quote(s string) string { return "`" + strings.ReplaceAll(s, "`", "``") + "`" }
 func quoted(xs []string) string {
 	out := make([]string, len(xs))
@@ -196,3 +421,21 @@ func quoted(xs []string) string {
 	}
 	return strings.Join(out, ", ")
 }
+
+func validAction(action string) bool {
+	switch strings.ToUpper(action) {
+	case "", "CASCADE", "SET NULL", "RESTRICT", "NO ACTION":
+		return true
+	}
+	return false
+}
+
+func unsupportedMode(mode string) string {
+	var modes []string
+	for _, unsupported := range []string{"NO_BACKSLASH_ESCAPES", "ANSI_QUOTES"} {
+		if strings.Contains(strings.ToUpper(mode), unsupported) {
+			modes = append(modes, unsupported)
+		}
+	}
+	return strings.Join(modes, ", ")
+}

pkg/writers/writer.go

@@ -56,6 +56,11 @@ const (
 
 // WriterOptions contains common options for writers
 type WriterOptions struct {
+	// StrictConversion rejects known lossy MySQL conversions before output or execution.
+	StrictConversion bool
+	// Warning receives conversion diagnostics. MySQL writes warnings to stderr when nil.
+	Warning func(string)
+
 	// OutputPath is the path where the output should be written
 	OutputPath string
 

tests/dbtest/README.md

@@ -22,7 +22,7 @@ Podman (preferred) or Docker. One tool for postgres, mssql, mysql.
 |---|---|---|---|---|
 | postgres | 5439 | `RELSPEC_TEST_PG_CONN` | `tests/postgres/init.sql` | readers/pgsql, writers/pgsql, writers/sqlexec |
 | mssql | 1439 | `RELSPEC_TEST_MSSQL_CONN` | `test_data/mssql/test_schema.sql` (creates `RelSpecTest`) | readers/mssql, writers/mssql |
-| mysql | 3309 | `RELSPEC_TEST_MYSQL_CONN` | `tests/dbtest/init/mysql.sql` | none (no Go driver/reader yet) |
+| mysql | 3309 | `RELSPEC_TEST_MYSQL_CONN` | `tests/dbtest/init/mysql.sql` | readers/mysql, writers/mysql |
 
 ## Env
 
@@ -43,3 +43,20 @@ Podman (preferred) or Docker. One tool for postgres, mssql, mysql.
 - Containers are named `relspec-test-<db>`; existing `tests/postgres/*.sh` and `make docker-*` use the same postgres name/port 5439 and remain independent.
 - mssql needs ~2GB RAM and takes longer to become ready.
 - Tests skip when the env var is unset.
+
+## MySQL schema fidelity tests
+
+Run `./tests/dbtest/dbtest.sh test mysql` for the MySQL 8.4 round-trip and
+unsupported-object regressions. They use temporary tables in `relspec_test`,
+including checks, functional indexes, composite foreign keys, binary/expression
+defaults, and generated columns. The test account needs table, view, and trigger
+privileges in that database. The disposable runner enables
+`log_bin_trust_function_creators` so binary logging does not require SUPER for
+trigger fixtures. For a separately managed test server, disable binary logging
+or configure that setting first. No global database-creation privilege is required.
+A failed or interrupted test can leave tables named `rt_*` or `unsupported_*`;
+restarting the disposable container removes them.
+
+See [the MySQL capability matrix](../../docs/MYSQL_FIDELITY.md) for the supported
+contract and strict conversion options. PostgreSQL/SQL Server tests remain
+separate; this suite does not certify MariaDB compatibility.

tests/dbtest/dbs/mysql.sh

@@ -8,9 +8,14 @@ DB_ENV=(-e MYSQL_ROOT_PASSWORD=relspec_root_password -e MYSQL_DATABASE=relspec_t
 DB_INIT_MOUNT="$ROOT/tests/dbtest/init/mysql.sql:/docker-entrypoint-initdb.d/init.sql"
 DB_CONN_VAR=RELSPEC_TEST_MYSQL_CONN
 DB_CONN="relspec:relspec_test_password@tcp(localhost:3309)/relspec_test"
-DB_DEFAULT_PKGS=""
+DB_DEFAULT_PKGS="./pkg/readers/mysql ./pkg/writers/mysql"
 
 db_ready()  { rt exec "$DB_CONTAINER" mysqladmin ping -h 127.0.0.1 -urelspec -prelspec_test_password --silent >/dev/null 2>&1; }
-db_post_init() { :; }
+# Configure the final server after readiness; SET GLOBAL during entrypoint init
+# only affects its temporary server and is reset before the tests connect.
+db_post_init() {
+    rt exec "$DB_CONTAINER" mysql -uroot -prelspec_root_password \
+        -e 'SET GLOBAL log_bin_trust_function_creators = 1' >/dev/null
+}
 db_shell()  { rt exec -it "$DB_CONTAINER" mysql -urelspec -prelspec_test_password relspec_test "$@"; }
 db_exec_file() { rt exec -i "$DB_CONTAINER" mysql -urelspec -prelspec_test_password relspec_test < "$1"; }

tests/dbtest/init/mysql.sql

@@ -1,5 +1,5 @@
 -- Minimal MySQL fixture for relspec container tests.
--- Extend when a MySQL reader/writer is added.
+-- Reader/writer live tests create additional temporary fixtures.
 CREATE TABLE users (
     id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
     email VARCHAR(255) NOT NULL,