Down commands

[Zevrap-81]

I wanted to ask why are down commands not supported?
is there a way to make them possible in case of a failed migration?

[zifter]

Hi @Zevrap-81 — good timing. down migrations were previously declined (#36) because ClickHouse has no transactional DDL, so there's no automatic rollback. But this has come up enough that I've changed my mind — I'm going to add explicit, hand-written down migrations (tracking in #68).

The plan: drop an optional {VERSION}_{name}.down.sql next to your migration, then run clickhouse-migrations down (--steps N / --to VERSION / --dry-run). It's deliberately naive — reversible changes (CREATE TABLE↔DROP TABLE, ADD COLUMN↔DROP COLUMN) roll back cleanly; destructive ones (data-losing drops, ALTER … DELETE/UPDATE mutations) stay your responsibility, since nothing can bring dropped data back.

Note: for a failed migration you often don't even need down — a migration is recorded only after its statements succeed, so a failed one just stays pending; fix the SQL and re-run.

[zifter]

Shipped in v0.13.0 🎉

pip install -U clickhouse-migrations, add an optional {VERSION}_{name}.down.sql next to your migration, and run clickhouse-migrations down (--steps N / --to VERSION / --dry-run). Docs: the Rollbacks section in the README.

It stays deliberately naive — reversible changes roll back cleanly, destructive ones (data-losing drops, ALTER … DELETE/UPDATE mutations) are your responsibility, since ClickHouse has no transactional DDL.

Thanks for the nudge, @Zevrap-81 — this had been declined before (#36) and your question tipped it over.