Empty ALTER TABLE when changing column type

[jvatic]

Changing a column's type generates a migration with an empty ALTER TABLE statement for that table, e.g.:

If running sql-schema schema generates

-- schema.sql
CREATE TABLE foo (
    bar INT
);

Then changing INT to TEXT (or anything else) and running sql-schema migration will generate a migration with an empty ALTER TABLE foo.

For PostgreSQL, it should generate something like

-- 002_alter_foo.up.sql
ALTER TABLE foo
    ALTER COLUMN bar SET DATA TYPE TEXT -- TODO: USING ...;