Re: Stats for multi-column indexes

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