SET CURRENT REFRESH AGE

The SET CURRENT REFRESH AGE statement changes the value of the CURRENT REFRESH AGE special register.

The CURRENT REFRESH AGE value corresponding to ANY (99 999 999 999 999) cannot be used in timestamp arithmetic operations because the result would be outside the valid range of dates.

Invocation

This statement can be embedded in an application program or issued interactively. It is an executable statement that can be dynamically prepared.

Authorization

None required.

Syntax


                            .-=-.                         
>>-SET CURRENT REFRESH AGE--+---+--+-numeric-constant-+--------><
                                   +-ANY--------------+   
                                   '-host-variable----'

Description

numeric-constant

A DECIMAL(20,6) value representing a timestamp duration. The value must be 0 or 99 999 999 999 999, the partial seconds of which is ignored and thus can be any value.

0: Indicates that query optimization using materialized query tables will not be attempted.
99999999999999: Indicates that any materialized query tables identified by the CURRENT MAINTAINED TABLE TYPES FOR OPTIMIZATION special register may be used to optimize the processing of a query. This value represents 9999 years, 99 months, 99 days, 99 hours, 99 minutes, and 99 seconds.

ANY

Shorthand for 99999999999999.

host-variable

A variable of type DECIMAL(20,6) or other type that is assignable to DECIMAL(20,6). It cannot be set to null. If host-variable has an associated indicator variable, the value of that indicator variable must not indicate a null value. The value of host-variable must be 0 or 99 999 999 999 999, the partial seconds of which is ignored and thus can be any value.

Notes

Materialized query tables created or altered with DISABLE QUERY OPTIMIZATION specified are not eligible for automatic query rewrite. Thus, they are not affected by the setting of this special register.

Setting the CURRENT REFRESH AGE special register to a value other than zero should be done with caution. Allowing a materialized query table that may not represent the values of the underlying base table to be used to optimize the processing of a query may produce results that do not accurately represent the data in the underlying table. This situation may be acceptable when you know the underlying data has not changed or you are willing to accept the degree of error in the results based on your knowledge of the data.

Examples

Example: Set the CURRENT REFRESH AGE special register to 99 999 999 999 999 to indicate that any materialized query tables identified by the CURRENT MAINTAINED TABLE TYPES FOR OPTIMIZATION special register can be used to optimize the processing of a query.

  SET CURRENT REFRESH AGE ANY;