SQL migration safety check for PostgreSQL, MySQL and SQLite

What it does

Reads migration files before they run in production and flags risky statements with the reason and a safer alternative. It never connects to a database.

• Data loss: DROP TABLE, DROP COLUMN, DROP DATABASE, TRUNCATE, UPDATE or DELETE without a top-level WHERE (a WHERE inside a sub-query does not count)
• Fails on tables with data: NOT NULL column without DEFAULT, SET NOT NULL, new UNIQUE, primary or foreign keys
• Locks and rewrites: column type changes, PostgreSQL index builds without CONCURRENTLY, CREATE INDEX CONCURRENTLY inside a transaction, constraints without NOT VALID, VACUUM FULL and more
• Breaks running code: table and column renames
• SQLite specifics: unsupported ALTER forms, non-constant defaults, table-rebuild pattern detection, PRAGMA foreign_keys
• Re-run failures: missing IF EXISTS or IF NOT EXISTS
• --big-tables raises severity for large tables; tables created in the same file and down migrations are lowered

How to use

python scripts/migration_check.py migrations/ --big-tables users,orders --json migration-review.json

The agent then checks table sizes, database version and code references, and proposes safe sequences such as expand and contract.

Requirements

• Python 3 (standard library only)

Caveats

• Static review: data-dependent failures (duplicates, NULLs) cannot be detected.
• Dialect detection is a guess; pass --dialect when you know it.
• It is not a full SQL parser, so unusual syntax may be split into statements incorrectly.