Add support for removing columns

[jverkoey]

Similar to try db.run(users.addColumn(suffix)), it would be useful to also be able to delete columns using syntax like try db.run(users.deleteColumn(suffix))

[jverkoey]

In the absence of such a function, something like the following can be ran:

try db.execute("""
    BEGIN TRANSACTION;
    ALTER TABLE your-table
    DROP COLUMN your-column;
    COMMIT TRANSACTION;
    """
)

[jberkel]

a future version will offer full support for schema migrations, it's not quite finished yet

[jverkoey]

Thank you! 🙏