Tom,
> Actually, I think you don't particularly need stats for that in most
> cases --- if the planner simply took note that the FK relationship
> exists, it would know that each row of the FK side joins to exactly
> one row of the PK side, which in typical cases is sufficient.
Is it? What about the other direction? Currently, doesn't the planner
assume that the rowcount relationship is 1 to ( child total rows /
parent total rows) ? That's ok for tables with relatively even
distribution, but not for skewed ones.
--Josh Berkus