Re: Use extended statistics to estimate (Var op Var) clauses

[Mark Dilger]

> On Aug 28, 2021, at 10:18 AM, Zhihong Yu <z...@yugabyte.com> wrote:
> 
> I wonder if the queries with (a=a) or (a<a) clauses are worth this additional 
> complexity to address.
> Has anyone seen such clause in production queries ?

You might expect clauses like WHERE FALSE to be unusual, but that phrase gets 
added quite a lot by query generators.  Somebody could add "WHERE a != a" in a 
misguided attempt to achieve the same thing.

I wouldn't be terribly surprised if query generators might generate queries 
with a variable number of tables joined together with comparisons between the 
joined tables, and in the degenerate case of only one table end up with a table 
column compared against itself.

You could argue that those people need to fix their queries/generators to not 
do this sort of thing, but the end user affected by such queries may have 
little ability to fix it.

—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company