CREATE TABLE entities (
  id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  -- Business fields
  name        VARCHAR(100) NOT NULL,
  code        VARCHAR(20) NOT NULL UNIQUE,
  status      VARCHAR(20) NOT NULL DEFAULT 'active'
    CHECK (status IN ('active', 'inactive', 'archived')),
  -- JSON for flexible metadata
  metadata    JSONB DEFAULT '{}',
  -- Audit fields
  created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
  updated_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
  deleted_at  TIMESTAMPTZ,  -- Soft delete
  created_by  UUID NOT NULL REFERENCES users(id),
  updated_by  UUID NOT NULL REFERENCES users(id)
);
 
-- Essential indexes
CREATE INDEX idx_entities_status ON entities(status) WHERE deleted_at IS NULL;
CREATE INDEX idx_entities_code ON entities(code);
CREATE INDEX idx_entities_created_at ON entities(created_at DESC);

-- UP Migration
-- Description: [What this migration does]
-- Reversible: YES
-- Data Loss: NONE
-- Estimated Duration: [expected runtime]
 
BEGIN;
  -- Schema changes here
  -- Data migrations here
COMMIT;
 
-- DOWN Migration (rollback)
BEGIN;
  -- Exact reverse of UP
COMMIT;

Is it a PK? → Auto-indexed
Is it a FK? → Always index
Used in WHERE? → Index it
Used in ORDER BY? → Consider index
Used in both WHERE + ORDER BY? → Composite index
High cardinality? → B-tree index
Low cardinality? → Consider partial index
Text search? → GIN/GiST index

-- Pagination: Use cursor-based for large tables
SELECT * FROM products
WHERE id > :last_seen_id
ORDER BY id ASC
LIMIT 20;
 
-- Aggregation: Pre-compute with materialized views
CREATE MATERIALIZED VIEW order_summary AS
SELECT
  customer_id,
  COUNT(*) as total_orders,
  SUM(total) as total_spent
FROM orders
GROUP BY customer_id;
 
-- Bulk operations: Use batch inserts
INSERT INTO products (name, sku, price)
SELECT name, sku, price FROM temp_import
ON CONFLICT (sku) DO UPDATE SET
  price = EXCLUDED.price,
  updated_at = NOW();

-- Check constraints for business rules
ALTER TABLE products ADD CONSTRAINT chk_positive_price
  CHECK (price >= 0);
 
-- Exclusion constraints for scheduling
ALTER TABLE bookings ADD CONSTRAINT excl_no_overlap
  EXCLUDE USING gist (
    room_id WITH =,
    daterange(start_date, end_date, '[]') WITH &&
  );
 
-- Partial unique index for soft delete
CREATE UNIQUE INDEX uq_products_sku_active
  ON products(sku) WHERE deleted_at IS NULL;
 
## When NOT to Use
 
**Do NOT use this skill when:**
- Writing application business logic (use domain-driven skill)
- Writing API endpoint implementations (use api-design skill)
- Reviewing code for quality issues (use code-review skill)
- Performing security audits (use security-auditor skill)
- Analyzing deployment configurations (use deployment skill)
- Writing SQL queries for specific databases (use sql-best-practices skill)
- Designing multi-page website layouts (use design-system skill)
- Reviewing git workflows (use git-workflow skill)