Re: pull-up subquery if JOIN-ON contains refs to upper-query

Hi! I found another example where the transformation worked incorrectly 
and reconsidered the idea.

As for conversion of exists_sublink_to_ANY, we need to get the flattened 
implicit-AND list of clauses and pull out the chunks of the WHERE clause 
that belong to the parent query,
since we are called halfway through the parent's preprocess_expression() 
and earlier steps of preprocess_expression() wouldn't get applied to the 
pulled-up stuff unless we do them here.
We also do some processing for vars depending on which side the var is 
on - if it's in a subquery, we only need to lower its level (varlevel) 
because subquery will be flatted, while
for other vars that belong to the parent query, we need to do 
preparation to pull up the sub-select into top range table.

For those expressions that we couldn't assign to either list, we define 
newWhere and apply both cases.

-- 
Regards,
Alena Rybakina
Postgres Professional