Gregory Stark <gsstark@xxxxxxx> writes: > Tom Lane <tgl@xxxxxxxxxxxxx> writes: >> only the a = 5 clause would be used with the index. As of 8.1 it will >> consider using nonconsecutive index columns > Really? Is this the "skip scan" plan people were pining for? No, there's no skip scan, it just applies all the indexable-column checks within the index instead of making a trip to the heap. For instance consider WHERE a >= 4 AND a < 7 AND c > 5 with index entries A B C 3 9 8 3 9 9 4 0 0 <- search starts here 4 0 1 reject ... 4 0 5 reject 4 0 6 accept (visit heap) 4 0 9 accept 4 1 0 reject ... 6 9 8 accept 6 9 9 accept 7 0 0 <- search ends when we reach here 7 0 1 If the condition on C is very selective then we might find ourselves scanning over a lot of rejected entries within the possible bounds for A. The problem is to guess whether re-descending the search tree will win compared to just slogging forward, and if so to generate a suitable search key for each intermediate descent. regards, tom lane
