| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
| Cc: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Aggregate ORDER BY patch |
| Date: | 2009-11-13 15:01:59 |
| Message-ID: | 2480.1258124519@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> On fre, 2009-11-13 at 03:16 +0000, Andrew Gierth wrote:
>> Caveat: as discussed earlier, this patch changes the behaviour of
>> array_agg(DISTINCT x) when applied to NULL inputs. Formerly, the NULLs
>> were unconditionally skipped; now, they are treated just like DISTINCT
>> or GROUP BY normally do.
> The right answer to that should be in the SQL standard.
It's not. The standard defines the behavior of certain specific
aggregates; it doesn't provide general rules that would apply to
user-defined aggregates. In particular, all the standard aggregates
are strict and so they just ignore nulls anyhow. The proposed change
would only affect the behavior of aggregates with non-strict transition
functions.
regards, tom lane
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