Re: Combining Aggregates

# select sum(x::numeric) from generate_series(1,3) x(x);

ERROR:  invalid memory alloc request size 18446744072025250716

The reason that this happens is down to the executor always thinking that Aggref returns the aggtype, but in cases where we're not finalizing the aggregate the executor needs to know that we're actually returning aggtranstype instead. Hash aggregates appear to work as the trans value is just stuffed into a hash table, but with plain and sorted aggregates this gets formed into a Tuple again, and forming a tuple naturally requires the types to be set correctly! I'm not sure exactly what the best way to fix this will be. I've hacked something up in the attached test patch which gets around the problem by adding a new aggtranstype to Aggref and also an 'aggskipfinalize'  field which I manually set to true in a bit of a hacky way inside the grouping planner. Then in exprType() for Aggref I conditionally return the aggtype or aggtranstype based on the aggskipfinalize setting.  This is most likely not the way to properly fix this, but I'm running out of steam today to think of how it should be done, so I'm currently very open to ideas on this.