A COMPOSITE index (ALSO called a concatenated index) is an index that you create on multiple columns in a table. Columns in a composite index can appear in any ORDER and need not be adjacent in the table. Composite indexes can speed retrieval of data for SELECT statements in which the WHERE clause references all or the leading portion of the columns in the composite index. THEREFORE, you should give some thought to the order of the columns used in the definition; generally, the most commonly accessed or most selective columns go first.

A composite index (also called a concatenated index) is an index that you create on multiple columns in a table. Columns in a composite index can appear in any order and need not be adjacent in the table. Composite indexes can speed retrieval of data for SELECT statements in which the WHERE clause references all or the leading portion of the columns in the composite index. Therefore, you should give some thought to the order of the columns used in the definition; generally, the most commonly accessed or most selective columns go first.