On Tue, 26 Feb 2019 at 11:51, Li, Zheng <zhe...@amazon.com> wrote:
> Resend the patch with a whitespace removed so that "git apply patch" works
> directly.
I had a quick look at this and it seems to be broken for the empty
table case I mentioned up thread.
Quick example:
Setup:
create table t1 (a int);
create table t2 (a int not null);
insert into t1 values(NULL),(1),(2);
select * from t1 where a not in(select a from t2);
Patched:
a
---
1
2
(2 rows)
Master:
a
---
1
2
(3 rows)
This will be due to the fact you're adding an a IS NOT NULL qual to
the scan of a:
postgres=# explain select * from t1 where a not in(select a from t2);
QUERY PLAN
------------------------------------------------------------------
Hash Anti Join (cost=67.38..152.18 rows=1268 width=4)
Hash Cond: (t1.a = t2.a)
-> Seq Scan on t1 (cost=0.00..35.50 rows=2537 width=4)
Filter: (a IS NOT NULL)
-> Hash (cost=35.50..35.50 rows=2550 width=4)
-> Seq Scan on t2 (cost=0.00..35.50 rows=2550 width=4)
(6 rows)
but as I mentioned, you can't do that as t2 might be empty and there's
no way to know that during planning.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
