Database Migration

Common Patterns

Adding a column (safe)

-- Up
ALTER TABLE users ADD COLUMN phone VARCHAR(20);

-- Down  
ALTER TABLE users DROP COLUMN phone;

Adding NOT NULL column (requires default)

-- Up
ALTER TABLE users ADD COLUMN status VARCHAR(20) DEFAULT 'active' NOT NULL;

-- Down
ALTER TABLE users DROP COLUMN status;

Renaming (use copy pattern for zero downtime)

-- Step 1: Add new column
ALTER TABLE users ADD COLUMN full_name VARCHAR(255);

-- Step 2: Copy data (in application or separate migration)
UPDATE users SET full_name = name;

-- Step 3: (Later) Drop old column
ALTER TABLE users DROP COLUMN name;

Adding index (concurrent for large tables)

-- PostgreSQL
CREATE INDEX CONCURRENTLY idx_users_email ON users(email);

Framework Detection

• db/migrate/ → Rails
• migrations/ or alembic/ → Python/SQLAlchemy
• prisma/migrations/ → Prisma
• drizzle/ → Drizzle

Match the project's migration format and naming convention.