Re: How can I re-use an expression in a SELECT?

I understand. Thanks very much!

RobR

From: Oliveiros d'Azevedo Cristina [mailto:oliveiros(dot)cristina(at)marktest(dot)pt]
Sent: Friday, July 06, 2012 9:30 AM
To: Rob Richardson; pgsql-novice(at)postgresql(dot)org
Subject: Re: [NOVICE] How can I re-use an expression in a SELECT?

I don't know any way of doing it without using a sub-query...

SELECT heat_time, cool_time, fire_date + interval '1 minute' * heat time as end_of_fire
FROM (
select charge,
case when c.rev_heat_time = 0 then c.pred_heat_time
else c.rev_heat_time
end as heat_time,
case when c.rev_cool_time = 0 then c.pred_cool_time
else c.rev_cool_time
end as cool_time
from charge c
) subquery

Surely there are more elegant ways of doing this in later versions.
I'm still using 8.3 ...

Best,
Oliveiros
----- Original Message -----
From: Rob Richardson<mailto:RDRichardson(at)rad-con(dot)com>
To: pgsql-novice(at)postgresql(dot)org<mailto:pgsql-novice(at)postgresql(dot)org>
Sent: Friday, July 06, 2012 2:04 PM
Subject: [NOVICE] How can I re-use an expression in a SELECT?

Greetings!

It seems to me, from my uneducated perspective, that if I have a calculated result with a name in a SELECT query, then I ought to be able to re-use the name later in the statement:

select charge,
case when c.rev_heat_time = 0 then c.pred_heat_time
else c.rev_heat_time
end as heat_time,
case when c.rev_cool_time = 0 then c.pred_cool_time
else c.rev_cool_time
end as cool_time,
fire_date + interval '1 minute' * heat_time as end_of_fire
from charge c

Of course, that fails because heat_time cannot be used to calculate end_of_fire. I would have to repeat the case statement that defines it instead. How can I avoid repeating complicated pieces of SELECT queries like this?

Thanks very much!

RobR