I’m currently working on a new project about the explain
For my research I’ve read a lot of documentations, presentations and blog posts and I would like to focus on the join type in the explain output.
And in particular when type=index in this explain output.
Take a look at what says the official documentation about type=index :
Wait a second, only the index tree is scanned? really?
This description seems to be the definition of a covering index.
But a covering index is only characterized by a “Using index” in the extra column of the explain output.
Consider the t1 table, just …[Read more]