feat: Enhance PostgreSQL type handling and migration scripts

- Introduced equivalent base types and variants for PostgreSQL types to normalize type comparisons.
- Added functions for normalizing SQL types and retrieving equivalent type variants.
- Updated migration writer to handle type alterations with checks for existing types.
- Implemented logic to create necessary extensions (e.g., pg_trgm) based on schema requirements.
- Enhanced tests to cover new functionality for type normalization and migration handling.
- Improved handling of GIN indexes to use appropriate operator classes based on column types.

cmd/relspec/merge.go

@@ -258,6 +258,11 @@ func runMerge(cmd *cobra.Command, args []string) error {
 	fmt.Fprintf(os.Stderr, "      ✓ Merge complete\n\n")
 	fmt.Fprintf(os.Stderr, "%s\n", merge.GetMergeSummary(result))
 
+	if strings.EqualFold(mergeOutputType, "pgsql") && len(result.TypeConflicts) > 0 {
+		return fmt.Errorf("merge detected conflicting existing column types and cannot safely continue with pgsql output\n%s",
+			merge.GetColumnTypeConflictSummary(result, 10))
+	}
+
 	// Step 4: Write output
 	fmt.Fprintf(os.Stderr, "\n[4/4] Writing output...\n")
 	fmt.Fprintf(os.Stderr, "      Format: %s\n", mergeOutputType)

cmd/relspec/merge_from_list_test.go

@@ -3,6 +3,7 @@ package main
 import (
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -160,3 +161,38 @@ func TestRunMerge_FromListMissingSourceType(t *testing.T) {
 		t.Error("expected error when neither --source-path nor --from-list is provided")
 	}
 }
+
+func TestRunMerge_PgsqlOutputRejectsColumnTypeConflict(t *testing.T) {
+	saved := saveMergeState()
+	defer restoreMergeState(saved)
+
+	dir := t.TempDir()
+	targetFile := filepath.Join(dir, "target.json")
+	sourceFile := filepath.Join(dir, "source.json")
+	writeTestJSONWithSingleColumnType(t, targetFile, "users", "integer")
+	writeTestJSONWithSingleColumnType(t, sourceFile, "users", "uuid")
+
+	mergeTargetType = "json"
+	mergeTargetPath = targetFile
+	mergeTargetConn = ""
+	mergeSourceType = "json"
+	mergeSourcePath = sourceFile
+	mergeSourceConn = ""
+	mergeFromList = nil
+	mergeOutputType = "pgsql"
+	mergeOutputPath = ""
+	mergeOutputConn = "postgres://relspec:secret@localhost/testdb"
+	mergeSkipTables = ""
+	mergeReportPath = ""
+
+	err := runMerge(nil, nil)
+	if err == nil {
+		t.Fatal("expected pgsql output merge to fail on column type conflict")
+	}
+	if !strings.Contains(err.Error(), "column type conflicts detected") {
+		t.Fatalf("expected conflict summary in error, got: %v", err)
+	}
+	if !strings.Contains(err.Error(), "public.users.id") {
+		t.Fatalf("expected conflicting column path in error, got: %v", err)
+	}
+}

cmd/relspec/testhelpers_test.go

@@ -71,6 +71,40 @@ func writeTestJSON(t *testing.T, path string, tableNames []string) {
 	}
 }
 
+func writeTestJSONWithSingleColumnType(t *testing.T, path, tableName, columnType string) {
+	t.Helper()
+
+	db := minimalDatabase{
+		Name: "test_db",
+		Schemas: []minimalSchema{{
+			Name: "public",
+			Tables: []minimalTable{{
+				Name:   tableName,
+				Schema: "public",
+				Columns: map[string]minimalColumn{
+					"id": {
+						Name:          "id",
+						Table:         tableName,
+						Schema:        "public",
+						Type:          columnType,
+						NotNull:       true,
+						IsPrimaryKey:  true,
+						AutoIncrement: true,
+					},
+				},
+			}},
+		}},
+	}
+
+	data, err := json.Marshal(db)
+	if err != nil {
+		t.Fatalf("failed to marshal test JSON: %v", err)
+	}
+	if err := os.WriteFile(path, data, 0644); err != nil {
+		t.Fatalf("failed to write test file %s: %v", path, err)
+	}
+}
+
 // convertState captures and restores all convert global vars.
 type convertState struct {
 	sourceType    string

pkg/merge/merge.go

@@ -22,6 +22,16 @@ type MergeResult struct {
 	EnumsAdded       int
 	ViewsAdded       int
 	SequencesAdded   int
+	TypeConflicts    []ColumnTypeConflict
+}
+
+// ColumnTypeConflict describes a column that exists in both schemas but with incompatible types.
+type ColumnTypeConflict struct {
+	Schema     string
+	Table      string
+	Column     string
+	TargetType string
+	SourceType string
 }
 
 // MergeOptions contains options for merge operations
@@ -146,11 +156,19 @@ func (r *MergeResult) mergeColumns(table *models.Table, srcTable *models.Table)
 
 	// Merge columns
 	for colName, srcCol := range srcTable.Columns {
-		if _, exists := existingColumns[colName]; !exists {
+		if tgtCol, exists := existingColumns[colName]; !exists {
 			// Column doesn't exist, add it
 			newCol := cloneColumn(srcCol)
 			table.Columns[colName] = newCol
 			r.ColumnsAdded++
+		} else if columnTypeConflict(tgtCol, srcCol) {
+			r.TypeConflicts = append(r.TypeConflicts, ColumnTypeConflict{
+				Schema:     firstNonEmpty(table.Schema, srcTable.Schema, srcCol.Schema),
+				Table:      firstNonEmpty(table.Name, srcTable.Name, srcCol.Table),
+				Column:     firstNonEmpty(tgtCol.Name, srcCol.Name, colName),
+				TargetType: describeColumnType(tgtCol),
+				SourceType: describeColumnType(srcCol),
+			})
 		}
 	}
 }
@@ -426,6 +444,52 @@ func cloneColumn(col *models.Column) *models.Column {
 	return newCol
 }
 
+func columnTypeConflict(target, source *models.Column) bool {
+	if target == nil || source == nil {
+		return false
+	}
+
+	return normalizeType(target.Type) != normalizeType(source.Type) ||
+		target.Length != source.Length ||
+		target.Precision != source.Precision ||
+		target.Scale != source.Scale
+}
+
+func normalizeType(value string) string {
+	return strings.ToLower(strings.TrimSpace(value))
+}
+
+func describeColumnType(col *models.Column) string {
+	if col == nil {
+		return ""
+	}
+
+	typeName := strings.TrimSpace(col.Type)
+	if typeName == "" {
+		return ""
+	}
+
+	switch {
+	case col.Precision > 0 && col.Scale > 0:
+		return fmt.Sprintf("%s(%d,%d)", typeName, col.Precision, col.Scale)
+	case col.Precision > 0:
+		return fmt.Sprintf("%s(%d)", typeName, col.Precision)
+	case col.Length > 0:
+		return fmt.Sprintf("%s(%d)", typeName, col.Length)
+	default:
+		return typeName
+	}
+}
+
+func firstNonEmpty(values ...string) string {
+	for _, value := range values {
+		if strings.TrimSpace(value) != "" {
+			return value
+		}
+	}
+	return ""
+}
+
 func cloneConstraint(constraint *models.Constraint) *models.Constraint {
 	if constraint == nil {
 		return nil
@@ -609,6 +673,7 @@ func GetMergeSummary(result *MergeResult) string {
 		fmt.Sprintf("Enums added:       %d", result.EnumsAdded),
 		fmt.Sprintf("Relations added:   %d", result.RelationsAdded),
 		fmt.Sprintf("Domains added:     %d", result.DomainsAdded),
+		fmt.Sprintf("Type conflicts:    %d", len(result.TypeConflicts)),
 	}
 
 	totalAdded := result.SchemasAdded + result.TablesAdded + result.ColumnsAdded +
@@ -625,3 +690,35 @@ func GetMergeSummary(result *MergeResult) string {
 
 	return summary
 }
+
+// GetColumnTypeConflictSummary returns a short, human-readable conflict summary.
+func GetColumnTypeConflictSummary(result *MergeResult, limit int) string {
+	if result == nil || len(result.TypeConflicts) == 0 {
+		return ""
+	}
+	if limit <= 0 {
+		limit = len(result.TypeConflicts)
+	}
+
+	lines := make([]string, 0, min(limit, len(result.TypeConflicts))+1)
+	lines = append(lines, "column type conflicts detected:")
+	for i, conflict := range result.TypeConflicts {
+		if i >= limit {
+			break
+		}
+		lines = append(lines, fmt.Sprintf("  - %s.%s.%s: target=%s source=%s",
+			conflict.Schema, conflict.Table, conflict.Column, conflict.TargetType, conflict.SourceType))
+	}
+	if len(result.TypeConflicts) > limit {
+		lines = append(lines, fmt.Sprintf("  ... and %d more", len(result.TypeConflicts)-limit))
+	}
+
+	return strings.Join(lines, "\n")
+}
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}

pkg/merge/merge_test.go

@@ -1,6 +1,7 @@
 package merge
 
 import (
+	"strings"
 	"testing"
 
 	"git.warky.dev/wdevs/relspecgo/pkg/models"
@@ -140,6 +141,61 @@ func TestMergeColumns_NewColumn(t *testing.T) {
 	}
 }
 
+func TestMergeColumns_TypeConflictIsDetected(t *testing.T) {
+	target := &models.Database{
+		Schemas: []*models.Schema{
+			{
+				Name: "public",
+				Tables: []*models.Table{
+					{
+						Name:   "users",
+						Schema: "public",
+						Columns: map[string]*models.Column{
+							"email": {Name: "email", Type: "varchar", Length: 255},
+						},
+					},
+				},
+			},
+		},
+	}
+	source := &models.Database{
+		Schemas: []*models.Schema{
+			{
+				Name: "public",
+				Tables: []*models.Table{
+					{
+						Name:   "users",
+						Schema: "public",
+						Columns: map[string]*models.Column{
+							"email": {Name: "email", Type: "text"},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	result := MergeDatabases(target, source, nil)
+
+	if len(result.TypeConflicts) != 1 {
+		t.Fatalf("Expected 1 type conflict, got %d", len(result.TypeConflicts))
+	}
+	conflict := result.TypeConflicts[0]
+	if conflict.Schema != "public" || conflict.Table != "users" || conflict.Column != "email" {
+		t.Fatalf("Unexpected conflict location: %+v", conflict)
+	}
+	if conflict.TargetType != "varchar(255)" {
+		t.Fatalf("Expected target type varchar(255), got %q", conflict.TargetType)
+	}
+	if conflict.SourceType != "text" {
+		t.Fatalf("Expected source type text, got %q", conflict.SourceType)
+	}
+
+	if got := target.Schemas[0].Tables[0].Columns["email"].Type; got != "varchar" {
+		t.Fatalf("Expected target column type to remain unchanged, got %q", got)
+	}
+}
+
 func TestMergeConstraints_NewConstraint(t *testing.T) {
 	target := &models.Database{
 		Schemas: []*models.Schema{
@@ -509,6 +565,9 @@ func TestGetMergeSummary(t *testing.T) {
 		ConstraintsAdded: 3,
 		IndexesAdded:     2,
 		ViewsAdded:       1,
+		TypeConflicts: []ColumnTypeConflict{
+			{Schema: "public", Table: "users", Column: "email", TargetType: "varchar(255)", SourceType: "text"},
+		},
 	}
 
 	summary := GetMergeSummary(result)
@@ -518,6 +577,9 @@ func TestGetMergeSummary(t *testing.T) {
 	if len(summary) < 50 {
 		t.Errorf("Summary seems too short: %s", summary)
 	}
+	if !strings.Contains(summary, "Type conflicts:    1") {
+		t.Errorf("Expected type conflict count in summary, got: %s", summary)
+	}
 }
 
 func TestGetMergeSummary_Nil(t *testing.T) {

pkg/pgsql/types_registry.go

@@ -145,6 +145,24 @@ var postgresTypeAliases = map[string]string{
 	"bool": "boolean",
 }
 
+var postgresEquivalentBaseTypes = map[string]string{
+	"character varying":           "varchar",
+	"character":                   "char",
+	"timestamp without time zone": "timestamp",
+	"timestamp with time zone":    "timestamptz",
+	"time without time zone":      "time",
+	"time with time zone":         "timetz",
+}
+
+var postgresEquivalentBaseTypeVariants = map[string][]string{
+	"varchar":     {"varchar", "character varying"},
+	"char":        {"char", "character"},
+	"timestamp":   {"timestamp", "timestamp without time zone"},
+	"timestamptz": {"timestamptz", "timestamp with time zone"},
+	"time":        {"time", "time without time zone"},
+	"timetz":      {"timetz", "time with time zone"},
+}
+
 // GetPostgresBaseTypes returns a sorted-ish stable list of registered base type names.
 func GetPostgresBaseTypes() []string {
 	result := make([]string, 0, len(postgresBaseTypes))
@@ -212,6 +230,86 @@ func CanonicalizeBaseType(baseType string) string {
 	return base
 }
 
+// EquivalentBaseType resolves broader SQL-equivalent spellings to a common comparable form.
+func EquivalentBaseType(baseType string) string {
+	base := CanonicalizeBaseType(baseType)
+	if equivalent, ok := postgresEquivalentBaseTypes[base]; ok {
+		return equivalent
+	}
+	return base
+}
+
+// NormalizeEquivalentSQLType returns a normalized SQL type string suitable for equality checks.
+// Equivalent spellings such as "character varying(255)" and "varchar(255)" normalize identically.
+func NormalizeEquivalentSQLType(sqlType string) string {
+	t := normalizeTypeToken(sqlType)
+	if t == "" {
+		return ""
+	}
+
+	arrayDepth := 0
+	for strings.HasSuffix(t, "[]") {
+		arrayDepth++
+		t = strings.TrimSpace(strings.TrimSuffix(t, "[]"))
+	}
+
+	modifier := ""
+	if idx := strings.Index(t, "("); idx >= 0 {
+		modifier = strings.TrimSpace(t[idx:])
+		t = strings.TrimSpace(t[:idx])
+	}
+
+	base := EquivalentBaseType(t)
+	normalized := base + modifier
+	for i := 0; i < arrayDepth; i++ {
+		normalized += "[]"
+	}
+	return normalized
+}
+
+// EquivalentSQLTypeVariants returns equivalent PostgreSQL spellings for a SQL type.
+// Examples:
+// - varchar(255) -> ["varchar(255)", "character varying(255)"]
+// - timestamptz -> ["timestamptz", "timestamp with time zone"]
+func EquivalentSQLTypeVariants(sqlType string) []string {
+	t := normalizeTypeToken(sqlType)
+	if t == "" {
+		return nil
+	}
+
+	arrayDepth := 0
+	for strings.HasSuffix(t, "[]") {
+		arrayDepth++
+		t = strings.TrimSpace(strings.TrimSuffix(t, "[]"))
+	}
+
+	modifier := ""
+	if idx := strings.Index(t, "("); idx >= 0 {
+		modifier = strings.TrimSpace(t[idx:])
+		t = strings.TrimSpace(t[:idx])
+	}
+
+	base := EquivalentBaseType(t)
+	bases := postgresEquivalentBaseTypeVariants[base]
+	if len(bases) == 0 {
+		bases = []string{base}
+	}
+
+	seen := make(map[string]bool, len(bases))
+	result := make([]string, 0, len(bases))
+	for _, variantBase := range bases {
+		variant := variantBase + modifier
+		for i := 0; i < arrayDepth; i++ {
+			variant += "[]"
+		}
+		if !seen[variant] {
+			seen[variant] = true
+			result = append(result, variant)
+		}
+	}
+	return result
+}
+
 // IsKnownPostgresType reports whether a type (including array forms) exists in the registry.
 func IsKnownPostgresType(sqlType string) bool {
 	base := CanonicalizeBaseType(ExtractBaseTypeLower(sqlType))

pkg/pgsql/types_registry_test.go

@@ -97,3 +97,51 @@ func TestPostgresTypeRegistry_TypeParsingAndCapabilities(t *testing.T) {
 		})
 	}
 }
+
+func TestNormalizeEquivalentSQLType(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{input: "character varying(255)", want: "varchar(255)"},
+		{input: "varchar(255)", want: "varchar(255)"},
+		{input: "timestamp with time zone", want: "timestamptz"},
+		{input: "timestamptz", want: "timestamptz"},
+		{input: "time without time zone", want: "time"},
+		{input: "character varying(255)[]", want: "varchar(255)[]"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			got := NormalizeEquivalentSQLType(tt.input)
+			if got != tt.want {
+				t.Fatalf("NormalizeEquivalentSQLType(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestEquivalentSQLTypeVariants(t *testing.T) {
+	tests := []struct {
+		input string
+		want  []string
+	}{
+		{input: "character varying(255)", want: []string{"varchar(255)", "character varying(255)"}},
+		{input: "timestamptz", want: []string{"timestamptz", "timestamp with time zone"}},
+		{input: "text[]", want: []string{"text[]"}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			got := EquivalentSQLTypeVariants(tt.input)
+			if len(got) != len(tt.want) {
+				t.Fatalf("EquivalentSQLTypeVariants(%q) len = %d, want %d (%v)", tt.input, len(got), len(tt.want), got)
+			}
+			for i := range tt.want {
+				if got[i] != tt.want[i] {
+					t.Fatalf("EquivalentSQLTypeVariants(%q)[%d] = %q, want %q", tt.input, i, got[i], tt.want[i])
+				}
+			}
+		})
+	}
+}

pkg/writers/pgsql/migration_writer.go

@@ -160,6 +160,17 @@ func (w *MigrationWriter) WriteMigration(model *models.Database, current *models
 func (w *MigrationWriter) generateSchemaScripts(model *models.Schema, current *models.Schema) ([]MigrationScript, error) {
 	scripts := make([]MigrationScript, 0)
 
+	if schemaRequiresPGTrgm(model) {
+		scripts = append(scripts, MigrationScript{
+			ObjectName: "extension.pg_trgm",
+			ObjectType: "create extension",
+			Schema:     model.Name,
+			Priority:   80,
+			Sequence:   len(scripts),
+			Body:       "CREATE EXTENSION IF NOT EXISTS pg_trgm;",
+		})
+	}
+
 	// Phase 1: Drop constraints and indexes that changed (Priority 11-50)
 	if current != nil {
 		dropScripts, err := w.generateDropScripts(model, current)
@@ -361,7 +372,7 @@ func (w *MigrationWriter) generateAlterTableScripts(schema *models.Schema, model
 				SchemaName: schema.Name,
 				TableName:  modelTable.Name,
 				ColumnName: modelCol.Name,
-				ColumnType: pgsql.ConvertSQLType(modelCol.Type),
+				ColumnType: effectiveColumnSQLType(modelCol),
 				Default:    defaultVal,
 				NotNull:    modelCol.NotNull,
 			})
@@ -380,12 +391,13 @@ func (w *MigrationWriter) generateAlterTableScripts(schema *models.Schema, model
 			scripts = append(scripts, script)
 		} else if !columnsEqual(modelCol, currentCol) {
 			// Column exists but properties changed
-			if modelCol.Type != currentCol.Type {
+			if !columnTypesEqual(modelCol, currentCol) {
 				sql, err := w.executor.ExecuteAlterColumnType(AlterColumnTypeData{
 					SchemaName: schema.Name,
 					TableName:  modelTable.Name,
 					ColumnName: modelCol.Name,
-					NewType:    pgsql.ConvertSQLType(modelCol.Type),
+					NewType:    effectiveAlterColumnSQLType(modelCol),
+					UsingExpr:  buildAlterColumnUsingExpression(modelCol.Name, effectiveAlterColumnSQLType(modelCol)),
 				})
 				if err != nil {
 					return nil, err
@@ -606,12 +618,11 @@ func buildIndexColumnExpressions(table *models.Table, index *models.Index, index
 		if table != nil {
 			if col, ok := resolveIndexColumn(table, colName); ok && col != nil {
 				colExpr = col.SQLName()
-				if strings.EqualFold(indexType, "gin") && isTextType(col.Type) {
+				if strings.EqualFold(indexType, "gin") {
-					opClass := extractOperatorClass(index.Comment)
+					opClass := ginOperatorClassForColumn(col, index.Comment)
-					if opClass == "" {
+					if opClass != "" {
-						opClass = "gin_trgm_ops"
+						colExpr = fmt.Sprintf("%s %s", col.SQLName(), opClass)
 					}
-					colExpr = fmt.Sprintf("%s %s", col.SQLName(), opClass)
 				}
 			}
 		}
@@ -875,11 +886,21 @@ func columnsEqual(col1, col2 *models.Column) bool {
 	if col1 == nil || col2 == nil {
 		return false
 	}
-	return strings.EqualFold(col1.Type, col2.Type) &&
+	return columnTypesEqual(col1, col2) &&
 		col1.NotNull == col2.NotNull &&
 		fmt.Sprintf("%v", col1.Default) == fmt.Sprintf("%v", col2.Default)
 }
 
+func columnTypesEqual(col1, col2 *models.Column) bool {
+	if col1 == nil || col2 == nil {
+		return false
+	}
+	return strings.EqualFold(
+		pgsql.NormalizeEquivalentSQLType(effectiveColumnSQLType(col1)),
+		pgsql.NormalizeEquivalentSQLType(effectiveColumnSQLType(col2)),
+	)
+}
+
 // constraintsEqual checks if two constraints are equal
 func constraintsEqual(c1, c2 *models.Constraint) bool {
 	if c1 == nil || c2 == nil {

pkg/writers/pgsql/migration_writer_test.go

@@ -97,6 +97,160 @@ func TestWriteMigration_ArrayDefault(t *testing.T) {
 	}
 }
 
+func TestWriteMigration_AltersColumnTypeWhenActualTypeDiffers(t *testing.T) {
+	current := models.InitDatabase("testdb")
+	currentSchema := models.InitSchema("public")
+	currentTable := models.InitTable("learnings", "public")
+	currentDetails := models.InitColumn("details", "learnings", "public")
+	currentDetails.Type = "jsonb"
+	currentTable.Columns["details"] = currentDetails
+	currentSchema.Tables = append(currentSchema.Tables, currentTable)
+	current.Schemas = append(current.Schemas, currentSchema)
+
+	model := models.InitDatabase("testdb")
+	modelSchema := models.InitSchema("public")
+	modelTable := models.InitTable("learnings", "public")
+	modelDetails := models.InitColumn("details", "learnings", "public")
+	modelDetails.Type = "text"
+	modelTable.Columns["details"] = modelDetails
+	modelSchema.Tables = append(modelSchema.Tables, modelTable)
+	model.Schemas = append(model.Schemas, modelSchema)
+
+	var buf bytes.Buffer
+	writer, err := NewMigrationWriter(&writers.WriterOptions{})
+	if err != nil {
+		t.Fatalf("Failed to create writer: %v", err)
+	}
+	writer.writer = &buf
+
+	if err := writer.WriteMigration(model, current); err != nil {
+		t.Fatalf("WriteMigration failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "ALTER TABLE public.learnings") || !strings.Contains(output, "ALTER COLUMN details TYPE text") {
+		t.Fatalf("expected migration to alter mismatched column type, got:\n%s", output)
+	}
+	if !strings.Contains(output, `ALTER COLUMN details TYPE text USING details::text;`) {
+		t.Fatalf("expected migration type alter to include USING cast, got:\n%s", output)
+	}
+}
+
+func TestWriteMigration_UsesStorageTypeForSerialAlterStatements(t *testing.T) {
+	current := models.InitDatabase("testdb")
+	currentSchema := models.InitSchema("public")
+	currentTable := models.InitTable("learnings", "public")
+	currentID := models.InitColumn("id", "learnings", "public")
+	currentID.Type = "uuid"
+	currentTable.Columns["id"] = currentID
+	currentSchema.Tables = append(currentSchema.Tables, currentTable)
+	current.Schemas = append(current.Schemas, currentSchema)
+
+	model := models.InitDatabase("testdb")
+	modelSchema := models.InitSchema("public")
+	modelTable := models.InitTable("learnings", "public")
+	modelID := models.InitColumn("id", "learnings", "public")
+	modelID.Type = "bigserial"
+	modelTable.Columns["id"] = modelID
+	modelSchema.Tables = append(modelSchema.Tables, modelTable)
+	model.Schemas = append(model.Schemas, modelSchema)
+
+	var buf bytes.Buffer
+	writer, err := NewMigrationWriter(&writers.WriterOptions{})
+	if err != nil {
+		t.Fatalf("Failed to create writer: %v", err)
+	}
+	writer.writer = &buf
+
+	if err := writer.WriteMigration(model, current); err != nil {
+		t.Fatalf("WriteMigration failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "ALTER COLUMN id TYPE bigint") {
+		t.Fatalf("expected serial alter to use bigint storage type, got:\n%s", output)
+	}
+	if strings.Contains(output, "ALTER COLUMN id TYPE bigserial;") {
+		t.Fatalf("did not expect invalid bigserial alter statement, got:\n%s", output)
+	}
+	if !strings.Contains(output, `ALTER COLUMN id TYPE bigint USING id::bigint;`) {
+		t.Fatalf("expected serial alter to include USING cast, got:\n%s", output)
+	}
+}
+
+func TestWriteMigration_ArrayAlterIncludesUsingCast(t *testing.T) {
+	current := models.InitDatabase("testdb")
+	currentSchema := models.InitSchema("public")
+	currentTable := models.InitTable("learnings", "public")
+	currentTags := models.InitColumn("tags", "learnings", "public")
+	currentTags.Type = "text"
+	currentTable.Columns["tags"] = currentTags
+	currentSchema.Tables = append(currentSchema.Tables, currentTable)
+	current.Schemas = append(current.Schemas, currentSchema)
+
+	model := models.InitDatabase("testdb")
+	modelSchema := models.InitSchema("public")
+	modelTable := models.InitTable("learnings", "public")
+	modelTags := models.InitColumn("tags", "learnings", "public")
+	modelTags.Type = "text[]"
+	modelTable.Columns["tags"] = modelTags
+	modelSchema.Tables = append(modelSchema.Tables, modelTable)
+	model.Schemas = append(model.Schemas, modelSchema)
+
+	var buf bytes.Buffer
+	writer, err := NewMigrationWriter(&writers.WriterOptions{})
+	if err != nil {
+		t.Fatalf("Failed to create writer: %v", err)
+	}
+	writer.writer = &buf
+
+	if err := writer.WriteMigration(model, current); err != nil {
+		t.Fatalf("WriteMigration failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, `ALTER COLUMN tags TYPE text[] USING tags::text[];`) {
+		t.Fatalf("expected array alter to include USING cast, got:\n%s", output)
+	}
+}
+
+func TestWriteMigration_DoesNotAlterEquivalentNormalizedColumnType(t *testing.T) {
+	current := models.InitDatabase("testdb")
+	currentSchema := models.InitSchema("public")
+	currentTable := models.InitTable("users", "public")
+	currentEmail := models.InitColumn("email", "users", "public")
+	currentEmail.Type = "character varying"
+	currentEmail.Length = 255
+	currentTable.Columns["email"] = currentEmail
+	currentSchema.Tables = append(currentSchema.Tables, currentTable)
+	current.Schemas = append(current.Schemas, currentSchema)
+
+	model := models.InitDatabase("testdb")
+	modelSchema := models.InitSchema("public")
+	modelTable := models.InitTable("users", "public")
+	modelEmail := models.InitColumn("email", "users", "public")
+	modelEmail.Type = "varchar(255)"
+	modelTable.Columns["email"] = modelEmail
+	modelSchema.Tables = append(modelSchema.Tables, modelTable)
+	model.Schemas = append(model.Schemas, modelSchema)
+
+	var buf bytes.Buffer
+	writer, err := NewMigrationWriter(&writers.WriterOptions{})
+	if err != nil {
+		t.Fatalf("Failed to create writer: %v", err)
+	}
+	writer.writer = &buf
+
+	if err := writer.WriteMigration(model, current); err != nil {
+		t.Fatalf("WriteMigration failed: %v", err)
+	}
+
+	output := buf.String()
+	if strings.Contains(output, "ALTER COLUMN email TYPE") {
+		t.Fatalf("did not expect alter type for equivalent normalized types, got:\n%s", output)
+	}
+}
+
 func TestWriteMigration_GinIndexOnTextUsesTrigramOperatorClass(t *testing.T) {
 	current := models.InitDatabase("testdb")
 	currentSchema := models.InitSchema("public")
@@ -132,6 +286,9 @@ func TestWriteMigration_GinIndexOnTextUsesTrigramOperatorClass(t *testing.T) {
 	}
 
 	output := buf.String()
+	if !strings.Contains(output, "CREATE EXTENSION IF NOT EXISTS pg_trgm;") {
+		t.Fatalf("expected trigram extension for text GIN migration index, got:\n%s", output)
+	}
 	if !strings.Contains(output, "USING gin (title gin_trgm_ops)") {
 		t.Fatalf("expected GIN text index to include gin_trgm_ops, got:\n%s", output)
 	}
@@ -212,14 +369,98 @@ func TestWriteMigration_GinIndexOnTextArrayDoesNotUseTrigramOperatorClass(t *tes
 	}
 
 	output := buf.String()
-	if !strings.Contains(output, "USING gin (tags)") {
+	if !strings.Contains(output, "USING gin (tags array_ops)") {
-		t.Fatalf("expected GIN array index without explicit trigram opclass, got:\n%s", output)
+		t.Fatalf("expected GIN array index with array_ops, got:\n%s", output)
 	}
 	if strings.Contains(output, "gin_trgm_ops") {
 		t.Fatalf("did not expect gin_trgm_ops for text[] migration index, got:\n%s", output)
 	}
 }
 
+func TestWriteMigration_GinIndexOnJSONBUsesJSONBOperatorClass(t *testing.T) {
+	current := models.InitDatabase("testdb")
+	currentSchema := models.InitSchema("public")
+	current.Schemas = append(current.Schemas, currentSchema)
+
+	model := models.InitDatabase("testdb")
+	modelSchema := models.InitSchema("public")
+
+	table := models.InitTable("learnings", "public")
+	detailsCol := models.InitColumn("details", "learnings", "public")
+	detailsCol.Type = "jsonb"
+	table.Columns["details"] = detailsCol
+
+	index := &models.Index{
+		Name:    "idx_learnings_details",
+		Type:    "gin",
+		Columns: []string{"details"},
+	}
+	table.Indexes[index.Name] = index
+
+	modelSchema.Tables = append(modelSchema.Tables, table)
+	model.Schemas = append(model.Schemas, modelSchema)
+
+	var buf bytes.Buffer
+	writer, err := NewMigrationWriter(&writers.WriterOptions{})
+	if err != nil {
+		t.Fatalf("Failed to create writer: %v", err)
+	}
+	writer.writer = &buf
+
+	if err := writer.WriteMigration(model, current); err != nil {
+		t.Fatalf("WriteMigration failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "USING gin (details jsonb_ops)") {
+		t.Fatalf("expected GIN jsonb index to include jsonb_ops, got:\n%s", output)
+	}
+	if strings.Contains(output, "gin_trgm_ops") {
+		t.Fatalf("did not expect gin_trgm_ops for jsonb migration index, got:\n%s", output)
+	}
+}
+
+func TestWriteMigration_GinIndexOnJSONBIgnoresIncompatibleTrigramOperatorClass(t *testing.T) {
+	current := models.InitDatabase("testdb")
+	currentSchema := models.InitSchema("public")
+	current.Schemas = append(current.Schemas, currentSchema)
+
+	model := models.InitDatabase("testdb")
+	modelSchema := models.InitSchema("public")
+
+	table := models.InitTable("learnings", "public")
+	detailsCol := models.InitColumn("details", "learnings", "public")
+	detailsCol.Type = "jsonb"
+	table.Columns["details"] = detailsCol
+
+	index := &models.Index{
+		Name:    "idx_learnings_details",
+		Type:    "gin",
+		Columns: []string{"details"},
+		Comment: "gin_trgm_ops",
+	}
+	table.Indexes[index.Name] = index
+
+	modelSchema.Tables = append(modelSchema.Tables, table)
+	model.Schemas = append(model.Schemas, modelSchema)
+
+	var buf bytes.Buffer
+	writer, err := NewMigrationWriter(&writers.WriterOptions{})
+	if err != nil {
+		t.Fatalf("Failed to create writer: %v", err)
+	}
+	writer.writer = &buf
+
+	if err := writer.WriteMigration(model, current); err != nil {
+		t.Fatalf("WriteMigration failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "USING gin (details jsonb_ops)") {
+		t.Fatalf("expected incompatible trigram hint on jsonb to fall back to jsonb_ops, got:\n%s", output)
+	}
+}
+
 func TestWriteMigration_WithAudit(t *testing.T) {
 	// Current database (empty)
 	current := models.InitDatabase("testdb")

pkg/writers/pgsql/templates.go

@@ -95,6 +95,16 @@ type AlterColumnTypeData struct {
 	TableName  string
 	ColumnName string
 	NewType    string
+	UsingExpr  string
+}
+
+type AlterColumnTypeWithCheckData struct {
+	SchemaName      string
+	TableName       string
+	ColumnName      string
+	NewType         string
+	EquivalentTypes string
+	UsingExpr       string
 }
 
 // AlterColumnDefaultData contains data for alter column default template
@@ -302,6 +312,15 @@ func (te *TemplateExecutor) ExecuteAlterColumnType(data AlterColumnTypeData) (st
 	return buf.String(), nil
 }
 
+func (te *TemplateExecutor) ExecuteAlterColumnTypeWithCheck(data AlterColumnTypeWithCheckData) (string, error) {
+	var buf bytes.Buffer
+	err := te.templates.ExecuteTemplate(&buf, "alter_column_type_with_check.tmpl", data)
+	if err != nil {
+		return "", fmt.Errorf("failed to execute alter_column_type_with_check template: %w", err)
+	}
+	return buf.String(), nil
+}
+
 // ExecuteAlterColumnDefault executes the alter column default template
 func (te *TemplateExecutor) ExecuteAlterColumnDefault(data AlterColumnDefaultData) (string, error) {
 	var buf bytes.Buffer

pkg/writers/pgsql/templates/alter_column_type.tmpl

@@ -1,2 +1,2 @@
 ALTER TABLE {{qual_table .SchemaName .TableName}}
-  ALTER COLUMN {{quote_ident .ColumnName}} TYPE {{.NewType}};
+  ALTER COLUMN {{quote_ident .ColumnName}} TYPE {{.NewType}}{{if .UsingExpr}} USING {{.UsingExpr}}{{end}};

pkg/writers/pgsql/templates/alter_column_type_with_check.tmpl

@@ -0,0 +1,22 @@
+DO $$
+DECLARE
+  current_type text;
+BEGIN
+  SELECT pg_catalog.format_type(a.atttypid, a.atttypmod)
+    INTO current_type
+  FROM pg_attribute a
+  JOIN pg_class t ON t.oid = a.attrelid
+  JOIN pg_namespace n ON n.oid = t.relnamespace
+  WHERE n.nspname = '{{.SchemaName}}'
+    AND t.relname = '{{.TableName}}'
+    AND a.attname = '{{.ColumnName}}'
+    AND a.attnum > 0
+    AND NOT a.attisdropped;
+
+  IF current_type IS NOT NULL
+     AND current_type <> ALL(ARRAY[{{.EquivalentTypes}}]) THEN
+    ALTER TABLE {{qual_table .SchemaName .TableName}}
+      ALTER COLUMN {{quote_ident .ColumnName}} TYPE {{.NewType}}{{if .UsingExpr}} USING {{.UsingExpr}}{{end}};
+  END IF;
+END;
+$$;

pkg/writers/pgsql/writer.go

@@ -143,6 +143,10 @@ func (w *Writer) GenerateSchemaStatements(schema *models.Schema) ([]string, erro
 		statements = append(statements, fmt.Sprintf("CREATE SCHEMA IF NOT EXISTS %s", schema.SQLName()))
 	}
 
+	if schemaRequiresPGTrgm(schema) {
+		statements = append(statements, `CREATE EXTENSION IF NOT EXISTS pg_trgm`)
+	}
+
 	// Phase 2: Create sequences
 	for _, table := range schema.Tables {
 		pk := table.GetPrimaryKey()
@@ -181,6 +185,12 @@ func (w *Writer) GenerateSchemaStatements(schema *models.Schema) ([]string, erro
 	}
 	statements = append(statements, addColStmts...)
 
+	alterTypeStmts, err := w.GenerateAlterColumnTypeStatements(schema)
+	if err != nil {
+		return nil, fmt.Errorf("failed to generate alter column type statements: %w", err)
+	}
+	statements = append(statements, alterTypeStmts...)
+
 	// Phase 4: Primary keys
 	for _, table := range schema.Tables {
 		// First check for explicit PrimaryKeyConstraint
@@ -262,13 +272,10 @@ func (w *Writer) GenerateSchemaStatements(schema *models.Schema) ([]string, erro
 			for _, colName := range index.Columns {
 				colExpr := colName
 				if col, ok := resolveIndexColumn(table, colName); ok {
-					// For GIN indexes on text columns, add operator class
+					if strings.EqualFold(indexType, "gin") {
-					if strings.EqualFold(indexType, "gin") && isTextType(col.Type) {
+						if opClass := ginOperatorClassForColumn(col, index.Comment); opClass != "" {
-						opClass := extractOperatorClass(index.Comment)
+							colExpr = fmt.Sprintf("%s %s", colName, opClass)
-						if opClass == "" {
-							opClass = "gin_trgm_ops"
 						}
-						colExpr = fmt.Sprintf("%s %s", colName, opClass)
 					}
 				}
 				columnExprs = append(columnExprs, colExpr)
@@ -437,6 +444,33 @@ func (w *Writer) GenerateAddColumnStatements(schema *models.Schema) ([]string, e
 	return statements, nil
 }
 
+func (w *Writer) GenerateAlterColumnTypeStatements(schema *models.Schema) ([]string, error) {
+	statements := []string{}
+
+	statements = append(statements, fmt.Sprintf("-- Alter column types for schema: %s", schema.Name))
+
+	for _, table := range schema.Tables {
+		columns := getSortedColumns(table.Columns)
+		for _, col := range columns {
+			targetType := effectiveAlterColumnSQLType(col)
+			stmt, err := w.executor.ExecuteAlterColumnTypeWithCheck(AlterColumnTypeWithCheckData{
+				SchemaName:      schema.Name,
+				TableName:       table.Name,
+				ColumnName:      col.Name,
+				NewType:         targetType,
+				EquivalentTypes: equivalentTypeListSQL(targetType),
+				UsingExpr:       buildAlterColumnUsingExpression(col.Name, targetType),
+			})
+			if err != nil {
+				return nil, fmt.Errorf("failed to generate alter column type for %s.%s.%s: %w", schema.Name, table.Name, col.Name, err)
+			}
+			statements = append(statements, stmt)
+		}
+	}
+
+	return statements, nil
+}
+
 // GenerateAddColumnsForDatabase generates ALTER TABLE ADD COLUMN statements for the entire database
 func (w *Writer) GenerateAddColumnsForDatabase(db *models.Database) ([]string, error) {
 	statements := []string{}
@@ -489,31 +523,7 @@ func (w *Writer) generateCreateTableStatement(schema *models.Schema, table *mode
 func (w *Writer) generateColumnDefinition(col *models.Column) string {
 	parts := []string{col.SQLName()}
 
-	// Type with length/precision - convert to valid PostgreSQL type
+	parts = append(parts, effectiveColumnSQLType(col))
-	baseType := pgsql.ConvertSQLType(col.Type)
-	typeStr := baseType
-	hasExplicitTypeModifier := pgsql.HasExplicitTypeModifier(baseType)
-
-	// Only add size specifiers for types that support them
-	if !hasExplicitTypeModifier && col.Length > 0 && col.Precision == 0 {
-		if pgsql.SupportsLength(baseType) {
-			typeStr = fmt.Sprintf("%s(%d)", baseType, col.Length)
-		} else if isTextTypeWithoutLength(baseType) {
-			// Convert text with length to varchar
-			typeStr = fmt.Sprintf("varchar(%d)", col.Length)
-		}
-		// For types that don't support length (integer, bigint, etc.), ignore the length
-	} else if !hasExplicitTypeModifier && col.Precision > 0 {
-		if pgsql.SupportsPrecision(baseType) {
-			if col.Scale > 0 {
-				typeStr = fmt.Sprintf("%s(%d,%d)", baseType, col.Precision, col.Scale)
-			} else {
-				typeStr = fmt.Sprintf("%s(%d)", baseType, col.Precision)
-			}
-		}
-		// For types that don't support precision, ignore it
-	}
-	parts = append(parts, typeStr)
 
 	// NOT NULL
 	if col.NotNull {
@@ -535,6 +545,64 @@ func (w *Writer) generateColumnDefinition(col *models.Column) string {
 	return strings.Join(parts, " ")
 }
 
+func effectiveColumnSQLType(col *models.Column) string {
+	if col == nil {
+		return ""
+	}
+
+	baseType := pgsql.ConvertSQLType(col.Type)
+	typeStr := baseType
+	hasExplicitTypeModifier := pgsql.HasExplicitTypeModifier(baseType)
+
+	if !hasExplicitTypeModifier && col.Length > 0 && col.Precision == 0 {
+		if pgsql.SupportsLength(baseType) {
+			typeStr = fmt.Sprintf("%s(%d)", baseType, col.Length)
+		} else if isTextTypeWithoutLength(baseType) {
+			typeStr = fmt.Sprintf("varchar(%d)", col.Length)
+		}
+	} else if !hasExplicitTypeModifier && col.Precision > 0 {
+		if pgsql.SupportsPrecision(baseType) {
+			if col.Scale > 0 {
+				typeStr = fmt.Sprintf("%s(%d,%d)", baseType, col.Precision, col.Scale)
+			} else {
+				typeStr = fmt.Sprintf("%s(%d)", baseType, col.Precision)
+			}
+		}
+	}
+
+	return typeStr
+}
+
+func effectiveAlterColumnSQLType(col *models.Column) string {
+	typeStr := effectiveColumnSQLType(col)
+	switch strings.ToLower(strings.TrimSpace(typeStr)) {
+	case "smallserial":
+		return "smallint"
+	case "serial":
+		return "integer"
+	case "bigserial":
+		return "bigint"
+	default:
+		return typeStr
+	}
+}
+
+func buildAlterColumnUsingExpression(columnName, targetType string) string {
+	if strings.TrimSpace(columnName) == "" || strings.TrimSpace(targetType) == "" {
+		return ""
+	}
+	return fmt.Sprintf("%s::%s", quoteIdent(columnName), targetType)
+}
+
+func equivalentTypeListSQL(sqlType string) string {
+	variants := pgsql.EquivalentSQLTypeVariants(sqlType)
+	quoted := make([]string, 0, len(variants))
+	for _, variant := range variants {
+		quoted = append(quoted, fmt.Sprintf("'%s'", escapeQuote(variant)))
+	}
+	return strings.Join(quoted, ", ")
+}
+
 // WriteSchema writes a single schema and all its tables
 func (w *Writer) WriteSchema(schema *models.Schema) error {
 	if w.writer == nil {
@@ -546,6 +614,10 @@ func (w *Writer) WriteSchema(schema *models.Schema) error {
 		return err
 	}
 
+	if err := w.writeRequiredExtensions(schema); err != nil {
+		return err
+	}
+
 	// Phase 2: Create sequences (priority 80)
 	if err := w.writeSequences(schema); err != nil {
 		return err
@@ -561,6 +633,10 @@ func (w *Writer) WriteSchema(schema *models.Schema) error {
 		return err
 	}
 
+	if err := w.writeAlterColumnTypes(schema); err != nil {
+		return err
+	}
+
 	// Phase 4: Create primary keys (priority 160)
 	if err := w.writePrimaryKeys(schema); err != nil {
 		return err
@@ -661,6 +737,16 @@ func (w *Writer) writeCreateSchema(schema *models.Schema) error {
 	return nil
 }
 
+func (w *Writer) writeRequiredExtensions(schema *models.Schema) error {
+	if !schemaRequiresPGTrgm(schema) {
+		return nil
+	}
+
+	fmt.Fprintln(w.writer, "CREATE EXTENSION IF NOT EXISTS pg_trgm;")
+	fmt.Fprintln(w.writer)
+	return nil
+}
+
 // writeSequences generates CREATE SEQUENCE statements for identity columns
 func (w *Writer) writeSequences(schema *models.Schema) error {
 	fmt.Fprintf(w.writer, "-- Sequences for schema: %s\n", schema.Name)
@@ -754,6 +840,21 @@ func (w *Writer) writeAddColumns(schema *models.Schema) error {
 	return nil
 }
 
+func (w *Writer) writeAlterColumnTypes(schema *models.Schema) error {
+	fmt.Fprintf(w.writer, "-- Alter column types for schema: %s\n", schema.Name)
+
+	statements, err := w.GenerateAlterColumnTypeStatements(schema)
+	if err != nil {
+		return err
+	}
+	for _, stmt := range statements[1:] {
+		fmt.Fprint(w.writer, stmt)
+		fmt.Fprint(w.writer, "\n")
+	}
+
+	return nil
+}
+
 // writePrimaryKeys generates ALTER TABLE statements for primary keys
 func (w *Writer) writePrimaryKeys(schema *models.Schema) error {
 	fmt.Fprintf(w.writer, "-- Primary keys for schema: %s\n", schema.Name)
@@ -857,13 +958,11 @@ func (w *Writer) writeIndexes(schema *models.Schema) error {
 			for _, colName := range index.Columns {
 				if col, ok := resolveIndexColumn(table, colName); ok {
 					colExpr := col.SQLName()
-					// For GIN indexes on text columns, add operator class
+					if strings.EqualFold(index.Type, "gin") {
-					if strings.EqualFold(index.Type, "gin") && isTextType(col.Type) {
+						opClass := ginOperatorClassForColumn(col, index.Comment)
-						opClass := extractOperatorClass(index.Comment)
+						if opClass != "" {
-						if opClass == "" {
+							colExpr = fmt.Sprintf("%s %s", col.SQLName(), opClass)
-							opClass = "gin_trgm_ops"
 						}
-						colExpr = fmt.Sprintf("%s %s", col.SQLName(), opClass)
 					}
 					columnExprs = append(columnExprs, colExpr)
 				}
@@ -1250,25 +1349,101 @@ func isIntegerType(colType string) bool {
 }
 
 // isTextType checks if a column type is a text type (for GIN index operator class)
-func isTextType(colType string) bool {
+// func isTextType(colType string) bool {
-	textTypes := []string{"text", "varchar", "character varying", "char", "character", "string"}
+// 	textTypes := []string{"text", "varchar", "character varying", "char", "character", "string"}
-	lowerType := strings.ToLower(colType)
+// 	lowerType := strings.ToLower(colType)
-	if strings.HasSuffix(lowerType, "[]") {
+// 	if strings.HasSuffix(lowerType, "[]") {
-		return false
+// 		return false
-	}
+// 	}
-	for _, t := range textTypes {
+// 	for _, t := range textTypes {
-		if strings.HasPrefix(lowerType, t) {
+// 		if strings.HasPrefix(lowerType, t) {
-			return true
+// 			return true
-		}
+// 		}
-	}
+// 	}
-	return false
+// 	return false
-}
+// }
 
 // isTextTypeWithoutLength checks if type is text (which should convert to varchar when length is specified)
 func isTextTypeWithoutLength(colType string) bool {
 	return strings.EqualFold(colType, "text")
 }
 
+func ginOperatorClassForColumn(col *models.Column, comment string) string {
+	if col == nil {
+		return ""
+	}
+
+	sqlType := effectiveColumnSQLType(col)
+	baseType := pgsql.CanonicalizeBaseType(pgsql.ExtractBaseTypeLower(sqlType))
+	isArray := pgsql.IsArrayType(sqlType)
+	requested := extractOperatorClass(comment)
+
+	if requested != "" && ginOperatorClassCompatible(baseType, isArray, requested) {
+		return requested
+	}
+
+	if isArray {
+		return "array_ops"
+	}
+
+	switch {
+	case isTextGinBaseType(baseType):
+		return "gin_trgm_ops"
+	case baseType == "jsonb":
+		return "jsonb_ops"
+	default:
+		return requested
+	}
+}
+
+func ginOperatorClassCompatible(baseType string, isArray bool, opClass string) bool {
+	switch opClass {
+	case "gin_trgm_ops", "gin_bigm_ops":
+		return !isArray && isTextGinBaseType(baseType)
+	case "jsonb_ops", "jsonb_path_ops":
+		return !isArray && baseType == "jsonb"
+	case "array_ops":
+		return isArray
+	default:
+		return true
+	}
+}
+
+func isTextGinBaseType(baseType string) bool {
+	switch baseType {
+	case "text", "varchar", "character varying", "char", "character", "string", "citext", "bpchar":
+		return true
+	default:
+		return false
+	}
+}
+
+func schemaRequiresPGTrgm(schema *models.Schema) bool {
+	if schema == nil {
+		return false
+	}
+	for _, table := range schema.Tables {
+		if table == nil {
+			continue
+		}
+		for _, index := range table.Indexes {
+			if index == nil || !strings.EqualFold(index.Type, "gin") {
+				continue
+			}
+			for _, colName := range index.Columns {
+				col, ok := resolveIndexColumn(table, colName)
+				if !ok || col == nil {
+					continue
+				}
+				if ginOperatorClassForColumn(col, index.Comment) == "gin_trgm_ops" {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
 func resolveIndexColumn(table *models.Table, colName string) (*models.Column, bool) {
 	if table == nil {
 		return nil, false

pkg/writers/pgsql/writer_test.go

@@ -116,8 +116,8 @@ func TestWriteDatabase_GinIndexOnTextArrayDoesNotUseTrigramOperatorClass(t *test
 	}
 
 	output := buf.String()
-	if !strings.Contains(output, `USING gin (tags)`) {
+	if !strings.Contains(output, `USING gin (tags array_ops)`) {
-		t.Fatalf("expected GIN index on array column without explicit trigram opclass, got:\n%s", output)
+		t.Fatalf("expected GIN index on array column with array_ops, got:\n%s", output)
 	}
 	if strings.Contains(output, "gin_trgm_ops") {
 		t.Fatalf("did not expect gin_trgm_ops for text[] column, got:\n%s", output)
@@ -153,11 +153,51 @@ func TestWriteDatabase_GinIndexOnQuotedTextColumnUsesTrigramOperatorClass(t *tes
 	}
 
 	output := buf.String()
+	if !strings.Contains(output, `CREATE EXTENSION IF NOT EXISTS pg_trgm`) {
+		t.Fatalf("expected trigram extension for text GIN index, got:\n%s", output)
+	}
 	if !strings.Contains(output, `USING gin (name gin_trgm_ops)`) {
 		t.Fatalf("expected quoted text GIN index to include gin_trgm_ops, got:\n%s", output)
 	}
 }
 
+func TestWriteDatabase_GinIndexOnJSONBUsesJSONBOperatorClass(t *testing.T) {
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("public")
+
+	table := models.InitTable("learnings", "public")
+
+	detailsCol := models.InitColumn("details", "learnings", "public")
+	detailsCol.Type = "jsonb"
+	table.Columns["details"] = detailsCol
+
+	index := &models.Index{
+		Name:    "idx_learnings_details",
+		Type:    "gin",
+		Columns: []string{"details"},
+	}
+	table.Indexes[index.Name] = index
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+
+	var buf bytes.Buffer
+	writer := NewWriter(&writers.WriterOptions{})
+	writer.writer = &buf
+
+	if err := writer.WriteDatabase(db); err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, `USING gin (details jsonb_ops)`) {
+		t.Fatalf("expected GIN jsonb index to include jsonb_ops, got:\n%s", output)
+	}
+	if strings.Contains(output, "gin_trgm_ops") {
+		t.Fatalf("did not expect gin_trgm_ops for jsonb column, got:\n%s", output)
+	}
+}
+
 func TestWriteForeignKeys(t *testing.T) {
 	// Create a test database with two related tables
 	db := models.InitDatabase("testdb")
@@ -1018,3 +1058,82 @@ func TestWriteAddColumnStatements(t *testing.T) {
 		t.Errorf("Output missing DO block\nFull output:\n%s", output)
 	}
 }
+
+func TestWriteSchema_EmitsGuardedAlterColumnTypeStatements(t *testing.T) {
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("public")
+
+	table := models.InitTable("agent_skills", "public")
+
+	nameCol := models.InitColumn("name", "agent_skills", "public")
+	nameCol.Type = "character varying"
+	nameCol.Length = 255
+	table.Columns["name"] = nameCol
+
+	tagsCol := models.InitColumn("tags", "agent_skills", "public")
+	tagsCol.Type = "text[]"
+	table.Columns["tags"] = tagsCol
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+
+	var buf bytes.Buffer
+	writer := NewWriter(&writers.WriterOptions{})
+	writer.writer = &buf
+
+	if err := writer.WriteDatabase(db); err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "-- Alter column types for schema: public") {
+		t.Fatalf("expected alter column type section, got:\n%s", output)
+	}
+	if !strings.Contains(output, "pg_catalog.format_type") {
+		t.Fatalf("expected guarded live-type check, got:\n%s", output)
+	}
+	if !strings.Contains(output, "ALTER COLUMN name TYPE character varying(255)") {
+		t.Fatalf("expected guarded alter for character varying(255), got:\n%s", output)
+	}
+	if !strings.Contains(output, "ARRAY['varchar(255)', 'character varying(255)']") {
+		t.Fatalf("expected equivalent type spellings for varchar guard, got:\n%s", output)
+	}
+	if !strings.Contains(output, "ALTER COLUMN tags TYPE text[]") {
+		t.Fatalf("expected guarded alter for array type, got:\n%s", output)
+	}
+	if !strings.Contains(output, `ALTER COLUMN tags TYPE text[] USING tags::text[];`) {
+		t.Fatalf("expected guarded alter for array type to include USING cast, got:\n%s", output)
+	}
+}
+
+func TestWriteSchema_UsesStorageTypeForSerialAlterStatements(t *testing.T) {
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("public")
+
+	table := models.InitTable("learnings", "public")
+	idCol := models.InitColumn("id", "learnings", "public")
+	idCol.Type = "bigserial"
+	table.Columns["id"] = idCol
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+
+	var buf bytes.Buffer
+	writer := NewWriter(&writers.WriterOptions{})
+	writer.writer = &buf
+
+	if err := writer.WriteDatabase(db); err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "ALTER COLUMN id TYPE bigint") {
+		t.Fatalf("expected serial alter to use bigint storage type, got:\n%s", output)
+	}
+	if strings.Contains(output, "ALTER COLUMN id TYPE bigserial;") {
+		t.Fatalf("did not expect invalid bigserial alter statement, got:\n%s", output)
+	}
+	if !strings.Contains(output, `ALTER COLUMN id TYPE bigint USING id::bigint;`) {
+		t.Fatalf("expected serial alter to include USING cast, got:\n%s", output)
+	}
+}