Re: Expression Pruning in postgress

HarmeekSingh Bedi <harmeeksingh@gmail.com> writes:
>    In a plan where Node 1 is parent {say join) and Node 2 is child
> (say scan)  . If node 1 has a expression say foo(column) then scan
> will project 'column'  for sure and join will
>       evaluate foo(column).  Now if the node above join does not need
> column ? how does postgress remove the column from join's projection
> list .

See build_joinrel_tlist() in relnode.c.

> I am seeing that it does not in many
>       cases specially when sort appears above.

Please show a concrete example.
        regards, tom lane