Re: COALESCE implementation question

At 23:28 5/08/00 -0400, Tom Lane wrote:
>Philip Warner <pjw(at)rhyme(dot)com(dot)au> writes:
>>> Well, the standard is perfectly clear, isn't it? If V(1) has side
>>> effects then trying to optimize this into just one evaluation of V(1)
>>> will generate non-spec-compliant results.
>
>> At least with the new function manager, if I feel te need I can write a
>> 'CoalesceValues' function (at least for fixed numbers of parameters).
>
>Mmm ... not really. You could detect nulls all right, but a function-
>based version of COALESCE would evaluate *all* its arguments exactly
>once, which is certainly wrong.

Good point. Although in the specific case (two args, one of them constant),
it's not an issue. I guess I'll just have to live with double-evaluation,
and a COALESCE than can return NULL. Grumble grumble...

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