Re: BUG #8237: CASE Expression - Order of expression processing

2013/6/18 Andres Freund <andres(at)2ndquadrant(dot)com>:
> On 2013-06-18 13:17:14 +0000, andrea(at)lombardoni(dot)ch wrote:
>> template1=# SELECT CASE WHEN 1=0 THEN 0 ELSE 1/0 END;
>> ERROR: division by zero
>>
>>
>> In this case the CASE behaves as expected.
>>
>>
>> But in the following expression:
>>
>>
>> template1=# SELECT CASE WHEN (SELECT 0)=0 THEN 0 ELSE 1/0 END;
>> ERROR: division by zero
>
> Hrmpf. This is rather annoying. Const simplification processes all
> clauses and evaluates them if it can. Which is - as demonstrated above -
> broken. The only reason
> #= SELECT CASE WHEN 1=1 THEN 0 ELSE 1/0 END;
> works is that we abort even looking at further WHEN clauses if we know
> that one WHEN succeeds.
> So it seems we need to stop processing after finding a single WHEN
> that's not const? Does anybody have a better idea?

probably we should to evaluate constants under subtransaction, and
after exception, we should to stop precalculation of related
subexpression.

But it is slow :(

>
> Greetings,
>
> Andres Freund
>
> --
> Andres Freund http://www.2ndQuadrant.com/
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