I find MySQL’s error messages pretty annoying due to how vague they usually are.
SQL Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near blah blah blah at line #
Not helpful.
I was doing a very simple INSERT into a [...]

Discovered today that I was getting the wrong id back when trying to do insert_id() on a MySQL connection that previously ran a INSERT… ON DUPLICATE KEY UPDATE…. The problem is that ordinarily on inserts, LAST_INSERT_ID() returns the auto_increment value that was used in the insert. However, when the query updates instead because a key [...]

If you’re getting too many MySQL threads or Apache connections, and you would like to debug them, here are two possible ways to get the info you need:
Apache
fullstatus – Displays a full status report from mod_status. For this to work, you need to have mod_status enabled on your server [...]