smf

smf is a lightweight CLI tool for diffing database schemas from SQL dumps and generating (SQL) migration with breaking-change warnings and rollback.

It is intentionally config-free: you give it two schema files (old.sql, new.sql), it shows what changed and produces a migration script, as well as rollback.

smf is always in safe mode first, which means it won't drop table, or apply changes that can potentially result in data loss.

Status

• Supported dialects: MySQL with TiDB options (diff + migration generation + apply on your database)

Build

This repository currently uses a local Go module name (module smf), so the simplest workflow is building from source:

go build -o smf ./

Run directly:

go run . --help

Run tests:

go test ./...

CLI

Diff two schemas

./smf diff <old.sql> <new.sql>
./smf diff <old.sql> <new.sql> -o diff.txt

Tip: there are ready-to-use fixture, so you can test the behavior:

./smf diff test/data/mysql_schema_v1.sql test/data/mysql_schema_v2.sql

Generate a migration (MySQL)

./smf migrate <old.sql> <new.sql>
./smf migrate <old.sql> <new.sql> -o migration.sql

By default, smf runs in safe mode (non-destructive where possible):

• dropped tables are renamed to __smf_backup_* instead of DROP TABLE
• dropped columns are renamed to __smf_backup_* instead of DROP COLUMN

To allow destructive changes, pass --unsafe:

./smf migrate <old.sql> <new.sql> --unsafe -o migration.sql

Generate rollback SQL

smf can emit rollback SQL for the generated migration (to run separately):

./smf migrate <old.sql> <new.sql> -o migration.sql -r rollback.sql

Rollback generation is "best-effort". For example, a true DROP TABLE cannot be automatically restored without an external backup. Maybe we will do something for it later.

What smf detects today

The generator annotates output with warnings/breaking changes for schema operations such as:

• table/column drops (data loss)
• type changes (widening vs narrowing) and risky length shrinks
• NULL -> NOT NULL transitions and adding NOT NULL columns without defaults
• constraint/index additions/removals/modifications (PK/UK/FK/CHECK)
• charset/collation changes (table + column)
• heuristics for likely column renames (to preserve data via CHANGE COLUMN)

Known limitations

• smf operates on SQL schema dumps (DDL). It does not inspect live DB data.

Contributing

We welcome contributions! Please see CONTRIBUTING.md for guidelines on how to get started, our coding standards, and how to run tests.

• Core diff logic lives under internal/diff/.
• Dialect-specific generation lives under internal/dialect/ (MySQL implementation in internal/dialect/mysql/).
• Parser integration lives under internal/parser/.

If you add new behavior, please add/extend tests and prefer fixture-based regression tests.