Graham Davis <gdavis@xxxxxxxxxxxxxxx> writes: > How come an aggreate like that has to use a sequential scan? I know > that PostgreSQL use to have to do a sequential scan for all aggregates, > but there was support added to version 8 so that aggregates would take > advantage of indexes. Not in a GROUP BY context, only for the simple case. Per the comment in planagg.c: * We don't handle GROUP BY, because our current implementations of * grouping require looking at all the rows anyway, and so there's not * much point in optimizing MIN/MAX. The problem is that using an index to obtain the maximum value of ts for a given value of assetid is not the same thing as finding out what all the distinct values of assetid are. This could possibly be improved but it would take a considerable amount more work. It's definitely not in the category of "bug fix". regards, tom lane
