On Wednesday 01 December 2004 17:53, Ross Honniball wrote:
If someone can give me a good reason why this is so, it will stop it
annoying me so much.
I'm sure someone on the _MYSQL_ list will give you a jolly good reason or two.
--
Jason Wong - Gremlins Associates - www.gremlins.biz
Open
Very simply, because a clause
WHERE sales * cost 100
would look up to sales and cost in the expression as SELECT fields.
Your clause will wotk if you add sales and cost to the SELECT fields,
but that would not be economical:
- you don't need them in the result
- you will execute the caclulation
Yeah, I've asked this question myself a million times. It'd be very
useful and maybe some DB system knows how to do this, but for the most
part you just have to deal with this reality.
I believe that it's a matter of timing, really. You can't use the alias
in the WHERE clause because it hasn't
Ross,
If someone can give me a good reason why this is so, it will stop it
annoying me so much.
From the MySQL manual for version 4.0.16:
It is not allowed to use a column alias in a WHERE clause, because the column
value may not yet be determined when the WHERE clause is executed. See
