Re: Add support for (Var op Var) clause in extended MCV statistics

Another issue mentioned in [1] involves cases where the clause is in the 
form (A op A). In my view, this isn't related to the current patch, as 
it can be addressed by rewriting the clause, similar to transforming A = 
A into A IS NOT NULL. This adjustment would result in more accurate 
estimation.

[1]: 
https://www.postgresql.org/message-id/7C0F91B5-8A43-428B-8D31-556458720305%40enterprisedb.com

Ilia Evdokimov,
Tantor Labs LLC.