You can add and delete database indexes any time, so the design team does not need to decide which database columns to index while they design the Eval database. Because all tables in the Eval database have primary keys, each table already has one index associated with it. During the lifetime of the database, tables will need different indexes, depending on how the queries currently in use access data, and the database administrators add and delete indexes as the need arises. Sometimes they might add an index for a few specific queries and then remove it. The designers will not add indexes until they write the code and queries for the PT application; the following two topics describe the columns in the Eval database that are logical candidates for clustered or nonclustered indexes. This section includes a brief discussion of Eval table indexes because you can create indexes on a table as soon as you create the table.
SQL Server provides two types of indexes—clustered and nonclustered. This section describes how the designers can implement each type of index in the Eval database to improve its performance.