Function-Based Indexes

Function-based indexes contain one or more expressions as index keys.You can create indexes directly on functions and expressions.

Like computed columns, function-based indexes are helpful for user-defined ordering and decision-support system (DSS) applications, which frequently require intensive data manipulation. Function-based indexes simplify the tasks in these applications and improve performance.

Function-based indexes are similar to computed columns in that they both allow you to create indexes on expressions.

However, there are significant differences:

Before you can execute create index, you must enable the database option select into:

sp_dboption <dbname>, 'select into', true

See the Reference Manual: Commands and the Reference Manual: Procedures.

Related concepts
Computed Columns