We all remember the classical explanation about the indexes in the database and how they make the task easier to find the right lines. I'm sure most of you visualizes something like this:
image
It becomes clear right away that it takes much less effort to find two or three right lines throughout the data. It is brilliant, easy, and clear.

Personally, I always thought that there is no room for any improvement regarding this method until I got familiar with the clustered indexes. It turned out that the non-clustered indexes are not that perfect as I though.

So here are some questions: What is exactly a clustered index? Why is it better than the non-clustered one? What’s going on with it in MySQL?
Siera 16 may 2014, 14:08