I've just read a paper that says PostgreSQL doesn't do this. My reading of the code is that we *do* evaluate the HAVING clause prior to calculating the aggregates for it. I thought I'd check to resolve the confusion.
- - - If not, it seems fairly straightforward to push down some or all of a HAVING clause so that the qual clause is tested prior to aggregation, not after aggregation. This could, for certain queries, significantly reduce the amount of effort that the final Agg node performs. We might think about deeper push-down within the query, but since the Agg node already has the havingQual, it seems a straightforward act to decide whether to apply it before or after the aggregation. We already do find_unaggregated_cols(), so little additional analysis seems required. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
