Always use defensive programming patterns in migration scripts to ensure they can be executed multiple times without errors. This prevents failures during re-execution scenarios and makes migrations more robust. Key patterns to implement: - Use `CREATE TABLE IF NOT EXISTS` instead of `CREATE TABLE` - Use `ALTER TABLE ADD COLUMN IF NOT EXISTS` instead of `ALTER TABLE ADD COLUMN` - Apply similar defensive patterns to other DDL statements Example: ```sql -- Good: Idempotent migration CREATE TABLE IF NOT EXISTS "chat_groups" ( "id" text PRIMARY KEY NOT NULL, "title" text ); ALTER TABLE "messages" ADD COLUMN IF NOT EXISTS "group_id" text; -- Bad: Non-idempotent migration CREATE TABLE "chat_groups" ( "id" text PRIMARY KEY NOT NULL, "title" text ); ALTER TABLE "messages" ADD COLUMN "group_id" text; ``` This approach ensures migrations won't fail with "already exists" errors when run multiple times, which is common during development, testing, and deployment scenarios.