13.08.2013 11:28, Kjell Rilbe wrote: > > I fear that I know too little about the inner workings, but I'm a bit > surprised... I would have thought that this is what actually happens: > > Select Expression > -> Aggregate > -> Sort (unique) > -> Table "RDB$RELATIONS" Access By ID > -> Index "RDB$INDEX_0" Scan
The innermost index scan is actually sorting, it backs the GROUP BY clause. You example suggests that the stream is then reordered by the explicit sort node, but that's not the case. In fact, we have two (or more) independents sorts - one for GROUP BY and others are for DISTINCTs inside aggregate functions, they work with different fields. Dmitry ------------------------------------------------------------------------------ Get 100% visibility into Java/.NET code with AppDynamics Lite! It's a free troubleshooting tool designed for production. Get down to code-level detail for bottlenecks, with <2% overhead. Download for free and get started troubleshooting in minutes. http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
