Обсуждение: Re: BUG #18114: FULL JOIN is replaced by LEFT JOIN in plan
This is not a bug. The row is filtered by the WHERE clause.
Sorry for disturbing.
On Sat, Sep 16, 2023, 22:36 PG Bug reporting form <noreply@postgresql.org> wrote:
The following bug has been logged on the website:
Bug reference: 18114
Logged by: crvv
Email address: crvv.mail@gmail.com
PostgreSQL version: 16.0
Operating system: Linux
Description:
SELECT * FROM (VALUES (1)) AS t(id)
CROSS JOIN unnest('{1,2}'::int[]) AS a(x)
FULL JOIN unnest('{2,3}'::int[]) AS b(x) ON a.x = b.x
WHERE t.id = 1
Execute this SQL, I get the result
id | x | x
----+---+---
1 | 1 |
1 | 2 | 2
My expection is
id | x | x
----+---+---
1 | 1 |
1 | 2 | 2
| | 3
The query plan is
QUERY PLAN
-------------------------------------------------------------------
Nested Loop Left Join (cost=0.01..0.08 rows=1 width=12)
Join Filter: (a.x = b.x)
-> Function Scan on unnest a (cost=0.00..0.03 rows=1 width=8)
Filter: (1 = 1)
-> Function Scan on unnest b (cost=0.00..0.02 rows=2 width=4)
So I think the FULL JOIN is replaced by LEFT JOIN.
The following SQL statements both give me the expected result.
SELECT * FROM (VALUES (1)) AS t(id)
CROSS JOIN unnest('{1,2}'::int[]) AS a(x)
FULL JOIN unnest('{2,3}'::int[]) AS b(x) ON a.x = b.x;
SELECT * FROM (VALUES (1)) AS t(id), unnest('{1,2}'::int[]) AS a(x)
FULL JOIN unnest('{2,3}'::int[]) AS b(x) ON a.x = b.x
WHERE t.id = 1;
I can reproduce on PostgreSQL 16.0, 15.4 and 14.9.
On Sat, Sep 16, 2023 at 11:32:15PM +1000, W??i C??ngru?? wrote: > This is not a bug. The row is filtered by the WHERE clause. > Sorry for disturbing. > > On Sat, Sep 16, 2023, 22:36 PG Bug reporting form <noreply@postgresql.org> > wrote: > > The following bug has been logged on the website: > > Bug reference: 18114 > Logged by: crvv > Email address: crvv.mail@gmail.com > PostgreSQL version: 16.0 > Operating system: Linux > Description: > > SELECT * FROM (VALUES (1)) AS t(id) > CROSS JOIN unnest('{1,2}'::int[]) AS a(x) > FULL JOIN unnest('{2,3}'::int[]) AS b(x) ON a.x = b.x > WHERE t.id = 1 > > Execute this SQL, I get the result > id | x | x > ----+---+--- > 1 | 1 | > 1 | 2 | 2 > > My expection is > id | x | x > ----+---+--- > 1 | 1 | > 1 | 2 | 2 > | | 3 Your expectation is incorrect. Last record has null t.id (not 1), so it was filtered out by WHERE.
Yes, I also realized it. The result depends on the JOIN order and the comma changed the order. On Sun, Sep 17, 2023 at 3:06 AM Ilya Anfimov <ilan@tzirechnoy.com> wrote: > > On Sat, Sep 16, 2023 at 11:32:15PM +1000, W??i C??ngru?? wrote: > > This is not a bug. The row is filtered by the WHERE clause. > > Sorry for disturbing. > > > > On Sat, Sep 16, 2023, 22:36 PG Bug reporting form <noreply@postgresql.org> > > wrote: > > > > The following bug has been logged on the website: > > > > Bug reference: 18114 > > Logged by: crvv > > Email address: crvv.mail@gmail.com > > PostgreSQL version: 16.0 > > Operating system: Linux > > Description: > > > > SELECT * FROM (VALUES (1)) AS t(id) > > CROSS JOIN unnest('{1,2}'::int[]) AS a(x) > > FULL JOIN unnest('{2,3}'::int[]) AS b(x) ON a.x = b.x > > WHERE t.id = 1 > > > > Execute this SQL, I get the result > > id | x | x > > ----+---+--- > > 1 | 1 | > > 1 | 2 | 2 > > > > My expection is > > id | x | x > > ----+---+--- > > 1 | 1 | > > 1 | 2 | 2 > > | | 3 > > Your expectation is incorrect. > Last record has null t.id (not 1), so it was > filtered out by WHERE. > > >