Re: LEFT JOINs not optimized away when not needed

Moshe Jacobson <moshe(at)neadwerx(dot)com> writes:
> On Tue, Jul 8, 2014 at 3:47 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> AFAICS, the eight
>> un-removed joins are either joining to non-unique keys, or can't be
>> removed because their tables are needed to provide joining columns for
>> un-removable joins.

> My point is that even if the column to which we are joining is a non-unique
> key, there should be no need to look at that table if the output does not
> include any values from that table, and there are no filters on that
> table's values, and all output columns are in the GROUP BY. Is the planner
> not smart enough to notice this?

No. There is nothing about GROUP BY in the join removal logic.

regards, tom lane