Bug #45963 DWIM: Allow group functions in WHERE clause, by doing GROUP BY first
Submitted: 6 Jul 2009 8:48 Modified: 6 Jul 2009 10:41
Reporter: Chris Hennick Email Updates:
Status: Not a Bug Impact on me:
Category:MySQL Server: DML Severity:S4 (Feature request)
Version:5.0.75-0ubuntu10.2 (Ubuntu) OS:Any
Assigned to: CPU Architecture:Any
Tags: DWIM, GROUP BY, where

[6 Jul 2009 8:48] Chris Hennick
The following statement yields an error:

select name, max(allowed) from (copy_limit group by name) where max(allowed) < 4;

even though this statement is the intuitive way to accomplish what it intends.

How to repeat:
create table copy_limit (name varchar(50), place varchar(20), allowed int unsigned, primary key (name, place));
select name, max(allowed) from (copy_limit group by name) where max(allowed) < 4;

Suggested fix:
When not in strict SQL mode, treat the above statement as equivalent to:

select * from (select name, max(allowed) as max from copy_limit group by name) foo where max < 4;
[6 Jul 2009 8:50] Chris Hennick
tagging as "DWIM"
[6 Jul 2009 9:10] Valeriy Kravchuk
Check HAVING clause of SELECT statement (see http://dev.mysql.com/doc/refman/5.1/en/select.html for the details), please. I think it does exactly what you need, without any new syntax or subqueries in FROM clause.
[6 Jul 2009 10:22] Chris Hennick
Changing WHERE to HAVING does indeed work. So the simplest DWIM will probably just be to move the invalid WHERE terms to a HAVING clause (and, where necessary, split the query with a UNION).
[6 Jul 2009 10:41] Valeriy Kravchuk
So, looks like there is no real need to introduce any new syntax.