I have a simple SELECT query that joins 6 views together. These views only take data from one table so are not too complex. However, when I join these 6 views together the query runs incredibly slow, sometimes taking 40 mins to execute.

So, should I add indexes to these views to make the query run quicker? Or should I add the indexes to the tables beneath the views?

Additionally, which general columns should I add the indexes too? (There is a UserID, a SK, and a few date columns)