Greg Stark <gsstark@mit.edu> writes:
> nested loop
> index scan expecting 1 record
> merge join
> index scan on <col1,col2> where col1 = outer.foo and col2
> between a and b
> some other scan
> Ie, where the nested loop is a degenerate nested loop which only
> expects a single value and provides a parameter which allows some
> partial index to work or allows for some other index scan by providing
> a higher order key element?
Right. I don't see any particular reason to assume the inner path
is iterated only once, either. If the key value coming from the outer
path is sufficiently useful, this could be a win even with multiple
iterations, as compared to having to scan the whole of some large
relation or other ...
regards, tom lane
