>>>>> "Joe" == Joe Wildish <joe-postgresql....@elusive.cx> writes:
>> I haven't looked at the background of this, but if what you want to >> know is whether the aggregate function has the semantics of min() or >> max() (and if so, which) then the place to look is >> pg_aggregate.aggsortop. Joe> Thanks for the pointer. I've had a quick look at pg_aggregate, and Joe> back at my code, but I think there is more to it than just the Joe> sorting property. Specifically we need to know about the aggregate Joe> function when combined with connectors <, <=, < ANY, <= ANY, < ALL Joe> and <= ALL (and their equivalents with ">" and ">="). The presence of an aggsortop means "this aggregate function is interchangeable with (select x from ... order by x using OP limit 1)", with all of the semantic consequences that implies. Since OP must be the "<" or ">" member of a btree index opclass, the semantics of its relationships with other members of the same opfamily can be deduced from that. Joe> Also, it looks like COUNT and SUM don't have a sortop Right, because those currently have no semantics that PG needs to know about or describe. -- Andrew (irc:RhodiumToad)
