From: | Brian Hurt <bhurt(at)janestcapital(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-novice(at)postgresql(dot)org |
Subject: | Re: Generic hash function? |
Date: | 2006-12-03 21:47:40 |
Message-ID: | 457345FC.7020507@janestcapital.com |
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Lists: | pgsql-novice |
Tom Lane wrote:
>Brian Hurt <bhurt(at)janestcapital(dot)com> writes:
>
>
>>I'm trying to write a generic equals operator that works on type
>>anyelement,
>>
>>
>
>What for? You'd ultimately have to depend on the various actual input
>types' native equality operators, so I don't see what this'd buy except
>a layer of useless-seeming overhead. Also, it could only be hashable
>if the input type's equality is hashable, and we don't have any way to
>deal with a "sometimes hashable" equality operator.
>
> regards, tom lane
>
>
>
>
What I'd like to write is:
CREATE FUNCTION eqnull(anyelement, anyelement) RETURNS BOOLEAN AS $_$
SELECT
(CASE
WHEN $1 IS NULL AND $2 IS NULL THEN TRUE
WHEN ($1 IS NULL AND $2 IS NOT NULL)
OR ($1 IS NOT NULL AND $2 IS NULL)
THEN FALSE
ELSE $1 = $2
END
)
$_$ IMMUTABLE LANGUAGE SQL;
Which changes how nulls are handled. This makes writing certain kinds
of queries much easier and much more clear what the query is doing.
Am I going to need to create an operator class for every type?
Brian
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