I need some help analysing some simple t-sql execution plans. I have a table [User] with the following 3 columns:
Id(Primary Key), Username(nvarchar(50)), FirstName(nvarchar(50))
I have Created an Unique NonClustered Index for the Username column
The execution plan for a query filtering by FirstName:
select * from [User] where FirstName ='John'
shows a Clustered Index Scan with a total cost of 0,0033095
The execution plan for another query filtering by Username:
select * from [User] where Username = 'johndoe'
shows a nested loop containing an Index Seek followed by a Clustered Index Seek with a total cost of 0,00657038! this is twice as much as the cost of the previous query and I don't get it!
There is an index associated with the Username column and no index associated with FirstName, I would expect the second query to be faster.