Re: Evolving databases (eg deleting columns)

On Thu, Jul 25, 2002 at 05:19:18PM -0700, Christian H. Stork wrote:

> My question: How can I evolve databases (ie deleting columns,
> adding/changing/removing constraints, etc)?

You can use ALTER TABLE for adding & removing constraints. But you
can't delete columns.

You can leave the columns in, however. You can add a new column,
renaming the former column to something new (like colname_dead), and
name the new column to the name of the original column. Then do

UPDATE table SET colname=colname_dead;
UPDATE table SET colname_dead=NULL;

Then, make that column null always. There's very little overhead
attached to a column with all nulls (4 bytes? I think that's it.
There's a map that needs to be maintained, but that's it).

A

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