Database : Single-column index vs. multicolumn index

The two types of indexes are single-column indexes and multicolumn indexes. A single-column index is an index based on the values in one column of a table. A multicolumn index is an index based on the values in multiple columns of a table.

Organization of this subsection

(1) Creating a single-column index

(2) Creating a multicolumn index

(1) Creating a single-column index

A single-column index should be created when retrieval will be executed using one column only as the key.

(2) Creating a multicolumn index

A multicolumn index should be created in the cases discussed below.

(a) Retrieval of data that satisfies multiple conditions

A multicolumn index should be created when data satisfying multiple conditions is to be retrieved, such as when a complex-condition retrieval using the AND operator with multiple columns as the key is executed.

http://itdoc.hitachi.co.jp/manuals/3020/3020635200e/W3520279.HTM#ID00988