Re: function(contants) evaluated for every row

On Thu, Mar 10, 2011 at 7:32 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> Robert Haas wrote:
>> 2010/11/25 pasman pasma?ski <pasman(dot)p(at)gmail(dot)com>:
>> >>I've seen this as well be a performance issue, in particular with partitioned tables.
>> >>Out of habit I now write functions that always cache the value of the function in
>> >>a variable and use the variable in the actual query to avoid this particular "gotcha".
>> >
>> > subquery may be used to cache constants:
>> >
>> > SELECT a_date
>> > ?FROM test
>> > ?WHERE a_date=(SELECT current_date);
>> >
>> >
>> > "Seq Scan on test1 ?(cost=0.01..10.76 rows=5 width=4)"
>> > " ?Filter: (a_date = $0)"
>> > " ?InitPlan 1 (returns $0)"
>> > " ? ?-> ?Result ?(cost=0.00..0.01 rows=1 width=0)"
>>
>> Interesting.  So we pull a subquery out and treat it as an initplan,
>> but not a stable function?  Hmm...
>
> I assume this is _not_ a TODO.

Dunno, not sure.

--
Robert Haas
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