I think array_agg also keeps nulls - although the draft standard I
have seems to contradict itself about this...
Ian
2008/10/26 Jeff Davis <pgsql@j-davis.com>:
> Here is a patch to support two aggregate functions:
>
> 1) ARRAY_AGG() -- SQL 2008 standard behavior, returns NULL on no input,
> and skips NULL inputs.
>
> 2) ARRAY_ACCUM() -- Returns empty array on no input, and includes NULL
> inputs.
>
> These accumulate the result in a memory context that lives across calls
> to the state function, so it's reasonably efficient. On my old laptop it
> takes about 5s to generate an array of 1M elements -- not great, but at
> least it's linear.
>
> Although array_agg is the standard behavior, array_accum is important
> because otherwise you always lose the NULLs, and that's difficult to
> work around even with COALESCE.
>
> I added them as new native functions because ARRAY_AGG is in the
> standard, but if others think they should live elsewhere that's fine. I
> think that they are generally pretty useful functions for people using
> arrays.
>
> This patch is contributed by Truviso.
>
> Regards,
> Jeff Davis
>
>
>
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