Hi Josef,

Good write up. Just a bit surprised that you didnt get much into when to use a Included column covering index..ie Index selection.

I did notice that there was a sentence 'Anything that is in the where clause would be a key, anything in your select statement would be an included column.' Though it works at most of the cases, it could have better had it been explained bit more.

It would think twice before including a column which is very huge/including too many number of columns, or a frequently updated column. Perhaps this one can be a relevant read.

http://strictlysql.blogspot.com/2009/11/covering-index-include-nonkey-columns.html