Always use defensive SQL clauses like `IF NOT EXISTS` and `IF EXISTS` in migration scripts to make them idempotent and prevent failures when run multiple times or in different environments. This ensures migrations can be safely re-executed without causing errors due to existing schema elements. Example: ```sql -- Good: Uses IF NOT EXISTS to prevent errors ALTER TABLE payment_intent ADD COLUMN IF NOT EXISTS enable_overcapture BOOLEAN; -- Good: Uses IF EXISTS for safe removal ALTER TABLE subscription DROP COLUMN IF EXISTS profile_id; ``` When performing complex operations like column renaming or constraint modifications, understand that some operations require separate statements and cannot be nested within a single ALTER TABLE command.