Re: Confusing results with lateral references

On 2015/12/03 21:26, Ashutosh Bapat wrote:
> Session 1
> postgres=# begin;
> BEGIN
> postgres=# update t1 set val = 2 where val2 = 1;
> UPDATE 1
> 
> Session 2
> postgres=# select * from t1 left join t2 on (t1.val = t2.val) for update of
> t1;
> 
> query waits
> 
> Session 1
> postgres=# commit;
> COMMIT
> 
> 
> Session 2 query returns two rows
> select * from t1 left join t2 on (t1.val = t2.val) for update of t1;
>  val | val2 | val | val2
> -----+------+-----+------
>    2 |    1 |     |
>    2 |    1 |     |
> (2 rows)
> 
> It's confusing to see two rows from left join result when the table really
> has only a single row. Is this behaviour expected?

Maybe it is. Because the other table still has two (1, 1) rows, LockRows's
subplan would still produce two rows in result, no?

Thanks,
Amit