From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Thomas Lockhart <lockhart(at)fourpalms(dot)org> |
Cc: | PostgreSQL Hackers List <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Suggestions for implementing IS DISTINCT FROM? |
Date: | 2002-06-23 16:01:39 |
Message-ID: | 8708.1024848099@sss.pgh.pa.us |
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Thomas Lockhart <lockhart(at)fourpalms(dot)org> writes:
> I'm looking at implementing IS DISTINCT FROM, among other things.
> ...
> I was thinking to implement this by simply expanding these rules within
> gram.y to be a tree of comparison tests.
Please, please, do not do that. Make a new expression node tree type,
instead. We've made this mistake before (eg for BETWEEN) and I don't
want to do it again.
Aside from the points you make, a direct expansion approach cannot
reverse-list properly in rules/views, and it will force multiple
evaluations of arguments that should not be multiply evaluated.
Adding a new expression node tree type is not too difficult these days;
see for example Joe Conway's recent NullTest and BooleanTest additions.
I believe the existing expansions of row comparison operators
(makeRowExpr) should be replaced by specialized nodes, too. That would
give us a shot at implementing row '<', '>' comparisons in a
spec-compliant fashion...
regards, tom lane
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