On Sun, 2005-01-16 at 14:11 -0500, Tom Lane wrote: > Ragnar =?ISO-8859-1?Q?Hafsta=F0?= <gnari@xxxxxxxxx> writes: > > On Sun, 2005-01-16 at 17:45 +0100, Bo Lorentsen wrote: > >> Why not use the index scan for every row, is this a "limit" in the > >> planner ? I think there is something in the planner I don't understand :-) > > > the planner will just use the plan it estimates will be fastest. > > because of how indexscans work in postgresql, in this case it would be > > slower than a tablescan (assuming the function really is volatile) > > It has nothing to do with speed, it has to do with giving the correct > answer. We define "correct answer" as being the result you would get > from a naive interpretation of the SQL semantics --- that is, for every > row in the FROM table, actually execute the WHERE clause, and return the > rows where it produces TRUE. I should not have used the word 'indexscan'. I just meant that it would be less effective to use an index to look up each result of the volatile function than using a tablescan. It was clear that the function would have to be called for each row, but the OP was asking (I think) why the index was not used. gnari ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
