FAST DUAL

Description

Provides a more efficient implementation for statements which select a single-row result from DUAL such as SYSDATE, USER or arithmetic calculations

Versions

This operation is implemented in the following versions

Example

This example was developed using Oracle 10.2.0.1 on Linux

This example does not require any table definitions

The statement

    SELECT SYSDATE FROM dual;

generates the following execution plan

0     SELECT STATEMENT Optimizer=CHOOSE
1   0   FAST DUAL

If the "_fast_dual_enabled" parameter is set to FALSE (default TRUE) then the FAST DUAL operation is disabled. For example

    ALTER SESSION SET "_fast_dual_enabled" = FALSE;

Now the statement

    SELECT SYSDATE FROM dual;

generates the following execution plan

0     SELECT STATEMENT Optimizer=CHOOSE
1   0   TABLE ACCESS (FULL) OF 'DUAL'