Re: function(contants) evaluated for every row

2010/11/25 pasman pasmański <pasman.p@gmail.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...

--
Robert Haas
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