Just had a strange query happen that I thought I would share. I am by no means a Mysql expert, I know enough to usually write decent queries that are performant.
I had one today that was baffling me. First, I know this should be extracted into reusable code, but right now that’s not the plan. In one part of our system a query was happening pretty quickly. In a new part that I am working on it was taking forever, to the point I had to kill the query (after 30+ seconds) so that it didn’t bring the entire system down.
I was trying everything to figure out why one was worse than the other. They both seemed like terrible queries from first sight. I rearranged the WHERE clause so that they matched, and that didn’t fix the problem.
The good query had: ORDER BY dateadded desc, id
The bad query had: ORDER BY dateadded desc
I guess that is something to try when you have non performant queries. There was a subquery happening as well, so I think the order by may be helping the subquery.
It was just interesting to me and I thought I would share.