Expression-based indexes

By using the expression-based index capability of DB2®, you can create an index that is based on a general expression. You can enhance query performance if DB2 chooses the expression-based index.

Use expression-based indexes when you want an efficient evaluation of queries that involve a column-expression. In contrast to simple indexes, where index keys consist of a concatenation of one or more table columns that you specify, the index key values are not the same as values in the table columns. The values have been transformed by the expressions that you specify.

You can create the index by using the CREATE INDEX statement. If an index is created with the UNIQUE option, the uniqueness is enforced against the values that are stored in the index, not against the original column values.

DB2 does not use expression-based indexes for queries that use sensitive static scrollable cursors.