GilaMonster (6/3/2013)
Key columns, because the ordering of them may be useful to the optimizer and query processor. Very much depends on the rest of the index and the rest of the query though.
I also thought that it should be key column, but I did some tests and these tests shows that it will be better to include that column. Aslo SQL Server advice to create index with included column.
Did you do any tests about? Particullary for SQL Server 2012...