order by null for mysql

[richlv]

reading http://www.mysqlperformanceblog.com/...porary-tables/ , i noticed the following suggstion :

As you can see I'm using ORDER BY NULL clause as otherwise MySQL will sort the data after performing group by which is overhead we're not looking to measure. This is actually good trick to use for cases when you do not need GROUP BY results sorted - it can significantly improve performance in some cases.

zabbix uses quite some 'group by', but does not use 'oder by null' - would it make sense to add this at least to some clauses for performance reasons ?

[Alexei]

I read about this some time ago. I am not happy about making any changes without clear proof of their efficiency. Show me the numbers before and after the change!

Besides, and this is even more important, MySQL is one of several databases supported supported by ZABBIX. If we supported MySQL only, we would use tons of MySQL specific tricks. Unfortunately (well, fortunately), there are other database engines ZABBIX also uses and MySQL is just one of them. Keeping SQL code clean is very important!

[richlv]

I read about this some time ago. I am not happy about making any changes without clear proof of their efficiency. Show me the numbers before and after the change!

good call. i've limited testing capabilities, so i'll add this to my "maybe try this at some point" list

Besides, and this is even more important, MySQL is one of several databases supported supported by ZABBIX. If we supported MySQL only, we would use tons of MySQL specific tricks. Unfortunately (well, fortunately), there are other database engines ZABBIX also uses and MySQL is just one of them. Keeping SQL code clean is very important!

obviously. i wouldn't suggest doing something as a shortcut on a specific db engine - but gaining performance might be a good reason.
if somebody else feels like testing this... that would be nice.