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

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?

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services