Re: WITHIN GROUP patch

>>>>> "Vik" == Vik Fearing <vik.fearing@dalibo.com> writes:
Vik> I certainly want it.  I do not have a copy of the SQL standard,Vik> but I have full faith in the Andrew Gierth's
claimthat this isVik> part of it.
 

For reference, this is how I believe it matches up against the spec
(I'm working from the 2008 final):

10.9 <aggregate function>:
 <hypothetical set function> is intended to be implemented in this patch exactly as per spec.
 <inverse distribution function>: the spec defines two of these, PERCENTILE_CONT and PERCENTILE_DISC:
 PERCENTILE_CONT is defined in the spec for numeric types, in which case it returns an approximate numeric result, and
forinterval, in which case it returns interval. Our patch defines percentile_cont functions for float8 and interval
inputtypes, relying on implicit casting to float8 to handle other numeric input types.
 
 As an extension to the spec, we define a percentile_cont function that returns an array of percentile values in one
call,as suggested by some users.
 
 PERCENTILE_DISC is defined in the spec for the same types as _CONT. Our version on the other hand accepts any type
whichcan be sorted, and returns the same type. This does mean that our version may return an exact numeric type rather
thanan approximate one, so this is a possible slight deviation from the spec.
 
 i.e. our  percentile_disc(float8) within group (order by bigint) returns a bigint, while the spec seems to imply it
shouldreturn an approximate numeric type (i.e. float*).
 
 Again, we additionally provide an array version which is not in the spec.
 mode() is not in the spec, we just threw it in because it was easy.

6.10 <window function>
 The spec says that <hypothetical set function> is not allowed as a window function.
 The spec does not forbid other <ordered set function>s in a window function call, but we have NOT attempted to
implementthis (largely for the same reasons that DISTINCT and ORDER BY are not implemented for aggregates as window
functions).

Conformance:  all the relevant features are parts of T612, "Advanced
OLAP Operations", which we already list in the docs on the unsupported
list with the comment "some forms supported". Maybe that could be
changed now to "most forms supported", but that's a subjective call
(and one we didn't really consider doing in this patch).

-- 
Andrew (irc:RhodiumToad)