Limit select on alembic_version to return only version_num

[maver1ck]

I want to use Alembic with Starrocks database.

To achieve this I need to patch alembic_version table with following code

def patch_alembic_version(context, **kwargs):
    migration_context = context._proxy._migration_context
    old_version = migration_context._version
    metadata = old_version.metadata
    metadata.remove(old_version)

    version = Table(
        'alembic_version',
        metadata,
        Column('id', types.BIGINT, autoincrement=True, primary_key=True),
        Column('version_num', types.VARCHAR(32), primary_key=False),
        starrocks_primary_key="id"
    )
    migration_context._version = version

This solution works with one exception - select on alembic_version always read version_num from first column.

Description

Fixes: sqlalchemy#1560

Checklist

This pull request is:

• A documentation / typographical error fix
  • Good to go, no issue or tests are needed
• A short code fix
  • please include the issue number, and create an issue if none exists, which
    must include a complete example of the issue. one line code fixes without an
    issue and demonstration will not be accepted.
  • Please include: Fixes: #<issue number> in the commit message
  • please include tests. one line code fixes without tests will not be accepted.
• A new feature implementation
  • please include the issue number, and create an issue if none exists, which must
    include a complete example of how the feature would look.
  • Please include: Fixes: #<issue number> in the commit message
  • please include tests.

Have a nice day!