checksum migrations (repeatable migrations)

[zy4]

Is this possibly a feature which others want to see in here as well?
The idea is to keep the migration file count small when there will be
frequent changes to views, functions or bulk data inserts.

Tracking and undoing migrations in this case would be handled by version control only.

Here is an example of this concept: https://flywaydb.org/documentation/concepts/migrations.html#repeatable-migrations

[dhui]

That's an interesting idea for creating reference data, functions, views, etc

Quoting relevant content in case the link above changes:

Repeatable migrations have a description and a checksum, but no version. Instead of being run just once, they are (re-)applied every time their checksum changes.

This is very useful for managing database objects whose definition can then simply be maintained in a single file in version control. They are typically used for

• (Re-)creating views/procedures/functions/packages/…
• Bulk reference data reinserts

Within a single migration run, repeatable migrations are always applied last, after all pending versioned migrations have been executed. Repeatable migrations are applied in the order of their description.

It is your responsibility to ensure the same repeatable migration can be applied multiple times. This usually involves making use of CREATE OR REPLACE clauses in your DDL statements.

It'd be quite a bit of work to implement this in a backwards compatible manner. e.g. need to support old migration file names and migrate the schema version table.

See also: #179 and #278

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EDIT:
Loading repeatable migrations from a different source and track them in a separate schema migrations table could make backwards compatibility easier to tackle