Re: Support "Right Semi Join" plan shapes

Hi! Thank you for your work on this subject.

I have reviewed your patch and I think it is better to add an Assert for 
JOIN_RIGHT_SEMI to the ExecMergeJoin and ExecNestLoop functions to 
prevent the use of RIGHT_SEMI for these types of connections (NestedLoop 
and MergeJoin).
Mostly I'm suggesting this because of the set_join_pathlist_hook 
function, which is in the add_paths_to_joinrel function, which allows 
you to create a custom node. What do you think?

-- 
Regards,
Alena Rybakina
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company