How do you do a subselect in the from clause?
Tom Lane wrote:
> Joseph Shraibman <[EMAIL PROTECTED]> writes:
>
>>playpen=# select a, sum(b) as dsum from taba where dsum > 5 group by(a);
>>ERROR: Attribute 'dsum' not found
>>
>
>>Why can we GROUP BY on an alias but not do a WHERE on an alias?
>>
>
> Because WHERE is computed before the select's output list is.
>
> Strictly speaking you shouldn't be able to GROUP on an alias either (the
> SQL spec doesn't allow it). We accept that for historical reasons only,
> ie, our interpretation of GROUP used to be wrong and we didn't want to
> break applications that relied on the wrong interpretation.
>
> Note that writing a GROUP on an alias does *not* mean the alias is only
> computed once. It saves no computation, only writing out the expression
> twice.
>
>
>>I have a subselect that
>>explain shows is being run twice if I have to put it in the WHERE clause.
>>
>
> Possibly you could restructure your query into something with a
> subselect in the FROM clause?
>
> regards, tom lane
>
--
Joseph Shraibman
[EMAIL PROTECTED]
Increase signal to noise ratio. http://www.targabot.com
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