Whenever I have a problem query in MySQL, I say to myself, I
know, I’ll use Explain Plan. Now I have two
problems. I run the explain plan, but then I have to look up all
the cryptic terms and read through the documentation to know what
in the world is going on. Well, over the weekend, I decided to
solve my own problem. I created a simple page that allows you to
run an explain plan, and then each of those obscure, abbreviated
terms is annotated with a tooltip that explains exactly what’s
going on. I’m calling it MySQL Explain Explained.
I created a demo using the sample employees database (which
you can download here). Here’s a sample query:
select gender, count(emp_no) as manager_cnt, sum(cnt) as sum, avg(cnt) as avg
from
(
select m.emp_no, m.gender, count(de.emp_no) as cnt
from …[Read more]