Re: Why can't I use an "AS" value in the WHERE clause.

[Pete Harlan]

On Mon, Apr 05, 2004 at 08:03:33PM -0500, Paul DuBois wrote:
> At 17:29 -0700 4/5/04, Daevid Vincent wrote:
> >I'm curious when will I be able to do something like this:
> >
> >SELECT *, IF(( (unix_timestamp()-unix_timestamp(last_seen)) < 600),1,0) as
> >active FROM wifi_table WHERE active = 1;
> 
> I think you'll never be able to do it.
> 
> The stuff after the SELECT is calculated based on the rows selected
> by the WHERE.  The WHERE therefore cannot be based on the stuff after
> the SELECT.

The parser has seen the 'as', though, and could expand it in the where
clause so the user doesn't have to do it (and do it correctly, and
maintain it in parallel).

The problem is MySQL can't just start doing this without breaking
queries that depend on it not happening.  (If the 'as' alias is the
same as a field name, for example.)

So I doubt it will happen, but not because it couldn't be done.

--Pete