Question

I have a Login Table that has a Identity field “Id” as the Primary Key(clustered) , and other fields like email , password etc.The only time I will use this table is to authenticate the user.After that i will be always querying other tables like user_profile, user_comments etc which has a foreign key Login_id to the Login Table.
My question is, is it a good idea to make the Login_id in the user_profile and user_comments table , a clustered index ? I will not be doing any join with the Login table since after the user is successfully authenticated, i will keep the LoginId in FormsAuthentication.SetAuthCookie for future querying the child tables.

I am developing a web app using C# and .Net.

Thanks in advance !

Answer 1

Since you will be constantly using the Login_id to get data from user_profile and user_comments, and assuming these searching using login_id in those tables will be more often than any other columns like Id, in those tables, then “login_id” should be clustered indexed . Basically, you would want to use the clustered index on column that gets queried the most. It could be two columns like “first name” and last name. From MSDN

It is important to define the clustered index key with as few columns
as possible. If a large clustered index key is defined, any
nonclustered indexes that are defined on the same table will be
significantly larger because the nonclustered index entries contain
the clustering key. The Index Tuning Wizard does not return an error
when saving an SQL script to a disk with insufficient available space.