On Wed, Apr 06, 2005 at 18:09:37 -0400, Tom Lane <[EMAIL PROTECTED]> wrote: > > Can anyone suggest a more general rule? Do we need for example to > consider whether the relation membership is the same in two clauses > that might be opposite sides of a range restriction? It seems like > > a.x > b.y AND a.x < b.z > > probably can be treated as a range restriction on a.x for this purpose, > but I'm much less sure that the same is true of > > a.x > b.y AND a.x < c.z > > Thoughts?
I think it makes sense to guess that a smaller fraction of the rows will be returned when a column value is bounded above and below than if it is only bounded on one side, even if the bounds aren't fixed. You can certainly be wrong. The difference between this and the normal case is that column statistics aren't normally going to be that useful. If date/time ranges are the common use for this construct, it might be better to create date and/or time range types that use rtree or gist indexes. ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
