Re: Smaller data types use same disk space

On Thu, Jul 26, 2012 at 11:02 AM, Mike Christensen <mike(at)kitchenpc(dot)com> wrote:
> I don't really think you'd need to decouple the internal column order
> from what the user sees. A REORDER COLUMNS command should re-build
> the table with the columns in the specified order. Internally, it
> should be no different from making a new table, copying all the data
> over, then deleting the old table. If there's any optimizations that
> can be done (such as making this faster on large tables), those could
> be done in future versions. I'd just like to changing column order
> easier without remaking the table or renaming columns and changing
> their data types (as suggested by Marc)

That's a controversial point: doing it that way makes reordering of
large tables highly impractical. A column map turns that into a
catalog update which can be done at any time. I would argue that you
can have it both ways: implement the map and have table rebuilding
operations (like TRUNCATE and CLUSTER) opportunistically do the
physical swap.

merlin