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Re: function(contants) evaluated for every row

From: pasman pasmański <pasman(dot)p(at)gmail(dot)com>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: function(contants) evaluated for every row
Date: 2010-11-25 09:57:26
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
>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)"



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