Added more examples and pgsql reader

tests/postgres/README.md

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+# PostgreSQL Integration Tests
+
+This directory contains Docker-based integration tests for the PostgreSQL reader.
+
+## Quick Start
+
+Run integration tests with Docker:
+
+```bash
+# From project root
+make docker-test
+```
+
+Or use the script directly:
+
+```bash
+./tests/postgres/run_tests.sh
+```
+
+## Manual Testing
+
+Start the PostgreSQL test database:
+
+```bash
+make docker-up
+```
+
+Run tests with the running database:
+
+```bash
+export RELSPEC_TEST_PG_CONN="postgres://relspec:relspec_test_password@localhost:5433/relspec_test"
+go test -v ./pkg/readers/pgsql/
+```
+
+Stop the database:
+
+```bash
+make docker-down
+```
+
+## Test Database Contents
+
+The test database (`relspec_test`) contains:
+
+### Schemas (3)
+- **public**: Main schema with user and blog data
+- **analytics**: Event tracking and analytics data
+- **inventory**: Product inventory management
+
+### Tables (14 total)
+- **public.users**: User accounts with various data types
+- **public.posts**: Blog posts with foreign keys
+- **public.comments**: Nested comments (self-referencing FK)
+- **public.categories**: Post categories
+- **public.post_categories**: Many-to-many junction table
+- **analytics.events**: Event tracking
+- **analytics.page_views**: Page view analytics
+- **analytics.conversions**: Conversion tracking
+- **inventory.products**: Product catalog
+- **inventory.warehouses**: Warehouse locations
+- **inventory.stock**: Product stock by warehouse
+
+### Views (8 total)
+- **public.active_users**: Active users only
+- **public.published_posts**: Published posts with author info
+- **public.post_stats**: Post statistics
+- **analytics.daily_stats**: Daily aggregated statistics
+- **analytics.top_pages**: Most viewed pages
+- **inventory.available_products**: Available products with stock
+- **inventory.low_stock_products**: Products with low inventory
+
+### Sequences (5 total)
+- **public.users_id_seq**: Users ID sequence
+- **public.posts_id_seq**: Posts ID sequence (with cycle)
+- **analytics.events_id_seq**: Events ID sequence
+- Plus auto-generated sequences for serial columns
+
+### Constraint Types
+- **Primary Keys**: All tables have PKs
+- **Foreign Keys**: Including cross-schema references
+- **Unique Constraints**: Username, email, SKU, etc.
+- **Check Constraints**: Age limits, status validation, balance checks
+
+### Index Types
+- **btree**: Standard B-tree indexes
+- **gin**: GIN indexes for JSONB and array columns
+- **hash**: Hash indexes for session lookups
+- **Unique**: Unique indexes
+- **Partial**: Conditional indexes (WHERE clauses)
+- **Composite**: Multi-column indexes
+
+## Connection Details
+
+- **Host**: localhost
+- **Port**: 5433 (to avoid conflicts with local PostgreSQL)
+- **Database**: relspec_test
+- **User**: relspec
+- **Password**: relspec_test_password
+
+Full connection string:
+```
+postgres://relspec:relspec_test_password@localhost:5433/relspec_test
+```
+
+## Requirements
+
+- Docker or Docker Compose
+- Go 1.25+
+
+## Makefile Targets
+
+- `make docker-up` - Start PostgreSQL container
+- `make docker-down` - Stop PostgreSQL container
+- `make docker-test` - Run full test suite with automatic cleanup
+- `make docker-test-integration` - Run integration tests only
+
+## Test Coverage
+
+The tests verify:
+- Schema introspection (excluding system schemas)
+- Table metadata extraction
+- View definitions and columns
+- Sequence properties and ownership
+- Column data types and constraints
+- Primary key detection
+- Foreign key relationships with referential actions
+- Unique and check constraints
+- Index types and definitions
+- Cross-schema relationships
+- Data type mapping
+- Error handling