Tom Lane wrote:
A larger objection to Jeff's draft patch is that it doesn't implement the <sort specification list>. I'm entirely happy about not doing that --- the current SQL committee's willingness to invent random new syntax and nonorthogonal behavior for every function they can think of will be the death of SQL yet --- but it's something that we at least need to document the workaround for.
How else will you tell an aggregate function whose result depends on the input order which order you want? The only aggregates defined in the standard where this matters are array_agg, array_accum, and xmlagg, but it would also be useful in other cases such as a text concatenation aggregate function or an aggregate function to calculate the correlation (or whatever alternative metric we come up with). Given that the standard does not provide for user-defined aggregates, I think the way it's specified is perfectly OK.
Without a way to control the order, how useful are these array aggregates really?
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