Data that needs to remain confidential within the database should be encrypted. Examples of confidential information are credit card numbers and employee salaries.
Data that is encrypted within columns can’t be read without having the proper credentials. Once data in a column is encrypted, the column can no longer be utilized in search arguments.
Columns can be encrypted using a passphrase, symmetric key, asymmetric key, or a certificate. Symmetric keys provide reasonably secure encryption while also providing the best possible performance.