Matthew Wakeling <matthew@flymine.org> writes:
> On Fri, 3 Apr 2009, Tom Lane wrote:
>> Not unless you have sorted the inputs in some way that has more
>> knowledge than the "equal" operator represents. Otherwise you can have
>> elements drop out that might still be needed to match to a later
>> left-hand element.
> Of course. You certainly have to choose a sort order that works. Sorting
> by the start field would be sufficient in this case.
Uh, no, it wouldn't. Visually:
L1 -------------------------
L2 -----------
L3 ---------------------
R1 --------
At L2, you'd conclude that you're done matching R1.
Intuitively, it seems like 1-D "overlaps" is a tractable enough
operator that you should be able to make something merge-like
work. But it's more complicated than I think you realize.
regards, tom lane