On Tue, 11 Apr 2006, Martijn van Oosterhout wrote:
Because there were no non-null rows, the system passed a NULL to the
final func. Seems you have two ways of dealing with this. Mark the
finalfunc as STRICT so the system won't call it with NULL. Or give the
agrregate an INITCOND which is an empty array. This would also avoid
the NULL.
Ah. Thanks, this might help for the original problem.
The problem in your example is that you're using aggrgates in the case
statement. Which means that as each row is processed, the aggregates
need to be calculated. It can't shortcut because if it first calculated
the max() and then the median() it would have to evaluate the entire
query twice.
A this sounds be reasonable. So my assumption might have been wrong.
In the general case, PostgreSQL *may* avoid calculating redundant
clauses if it doesn't need to, but you can't rely on it.
Just theoretically spoken: Woouldn't it make sense to enforce to
avoid this calculation.
Fixing your underlying issue with the aggregate should solve everything
for you.
Sure. I hope that I was able to trigger some ideas about optimisation
anyway.
Thanks for the quick help
Andreas.
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