> > If we want to do anything much smarter than that like trying every > combination of the GROUP BY clause, then plan times are likely going > to explode. The join order search is done based on the chosen query > pathkeys, which in many queries is the pathkeys for the GROUP BY > clause (see standard_qp_callback()). This means throughout the join > search, planner will try and form paths that provide pre-sorted input > that allows the group by to be implemented efficiently with pre-sorted > data. You might see Merge Joins rather than Hash Joins, for example. >
Are there guidelines or principles you could share about writing the group by clause such that it is more efficient?
