Creating Indexes on Encrypted Columns

You can create an index on an encrypted column if you specify the encryption key without any initialization vector or random padding. Indexes on encrypted columns are useful for equality and nonequality matches, but cannot be used to match case-insensitive data, or to perform range searches of any data.

To improve performance on both equality and nonequality searches, and on joins, create indexes on encrypted columns.

create index reports an error if you create:

A functional index using an expression that references an encrypted column
An index on a column encrypted with initialization vector or random padding

Note: You cannot use an encrypted column in an expression for a functional index.