Gregory Stark <stark@enterprisedb.com> writes:
> Merge Join (cost=100000149.78..100000448.70 rows=13161 width=36)
> Merge Cond: (a.a = "inner"."?column2?")
> -> Index Scan using aa on a (cost=0.00..62.45 rows=1230 width=32)
> -> Sort (cost=100000149.78..100000155.13 rows=2140 width=4)
> Sort Key: (b.b)::numeric
> -> Seq Scan on b (cost=100000000.00..100000031.40 rows=2140 width=4)
> That doesn't seem to even fit your description; the join is in fact on the
> unmodified inner variable here, no? Is this a bug?
No, the join condition is "a.a = b.b::numeric", because the only usable =
operator is numeric-eq-numeric. If we were to create a numeric-eq-int
operator then use of an indexscan on b would be possible. Whether this
is an issue in real-world usage is debatable, though. Certainly my
advice to anyone worried about the performance of such a join would be
to change the numeric column to an integer type --- without that you're
going to have performance problems anyway, just because numeric
arithmetic is slow.
regards, tom lane