Re: Identity projection

Hello. Sorry for long absence.

# I've lost my health and am not fully recovered..

The direction of the discussion now taken place is just what I've
wanted. The patch I proposed simply came from my poor
understanding about exact how to detect identity projection by
comparing tlists, and I couldn't found how to eliminate unwanted
nodes appropriately.

Thanks, Amit. I'll catch up this discussion soon.

amit.kapila> Amit kapila <amit.kapila@huawei.com> writes:
amit.kapila> >>> if (!is_projection_capable_plan(result_plan) && compare_tlist_exprs(sub_tlist,
result_plan->targetlist))
 
amit.kapila> 
amit.kapila> >> Sorry, the check I suggested in last mail should be as below:
amit.kapila> 
amit.kapila> >> if (!is_projection_capable_plan(result_plan) && !compare_tlist_exprs(sub_tlist,
result_plan->targetlist))
 
amit.kapila> 
amit.kapila> > You know, I was thinking that compare_tlist_exprs() was a pretty
amit.kapila> > unhelpfully-chosen name for a function returning boolean, and this
amit.kapila> > thinko pretty much proves the point.  It'd be better to call it
amit.kapila> > something like equivalent_tlists(), tlists_are_equivalent(), etc.
amit.kapila> > (I'm not caring for the emphasis on the exprs either, because I think
amit.kapila> > it'll also be necessary to compare resjunk fields for instance.)
amit.kapila> 
amit.kapila> The fields which cannot be compared are resname, resorigtbl, resorigcol as these gets cleared in planner.
amit.kapila> I am not sure about fields resno and ressortgroupref, but I will check in more detail before sending
patch.

With best regards,

-- 
Kyotaro Horiguchi