SQL Statement - How can Improve speed with indexing

Question

I have a script that has to look throught over 2.5 million records to find if a member that has an unread email. I want to know what can be done to improve its speed. Curr

Answer 1

Looks like a good candidate for a filtered index.

A filtered index is an optimized nonclustered index, especially suited to cover queries that select from a well-defined subset of data. It uses a filter predicate to index a portion of rows in the table. A well-designed filtered index can improve query performance, reduce index maintenance costs, and reduce index storage costs compared with full-table indexes.

Something along these lines:

CREATE NONCLUSTERED INDEX IX_MemberMail_ToMemberId_Unread
ON dbo.MemberMail (ToMemberId ASC)
WHERE ToReadFlag = 0
AND ToDeletedFlag = 0
AND FromDeletedFlag = 0
AND OnHold = 0
AND ToArchivedFlag = 0;