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SQL Optimizer for DB2 LUW 4.4.1 - Release Notes

Optimize the Original SQL Statement

Automatically Rewrite the Original SQL Statement

Use the SQL Rewrite function to generate alternatives to an SQL statement that you enter in the SQL Optimizer window or that you sent to SQL Optimizer from another tool, such the Scanned SQL Viewer, Toad Database Explorer, or SQL Formatter.

To rewrite an SQL statement

  1. Provide the SQL statement.

    Note: In Toad, if you open a SQL Optimizer session on the SQL used in a view, trigger, or MQ table, the statement automatically displays in the SQL Optimizer window.

  2. Click image\B_Optimize.gif to rewrite the original SQL. The rewrite time is dependent on the complexity of the original SQL statement, the SQL Options applied, and the quota values set in the Options window. When the rewrite completes, each rewritten SQL version displays as a SQL alternative in the Run Time pane.

Warning: When you define the optimization quota values that, note that the higher the quota, the longer it may take to rewrite a complicated SQL statement.

Note: The SQL Rewrite process executes multiple transformation rules to produce a list of semantically equivalent SQL alternatives, each with a unique access plan. SQL options defined in the Options window are also applied to produce the list of SQL alternatives.

To abort the rewrite process

Click image\B_AbortOptimize.gif.

Allow a few seconds to terminate all processes.

Automatically Start the Batch Run

If you have selected the Automatically start Batch Run after rewriting option, the Batch Run Criteria window automatically opens before the rewrite process begins so you can select the settings for the Batch Run.


  • To generate virtual index sets that you can add to the list of SQL alternatives generated during SQL Rewrite, click . You can then include these index-set alternatives in the Batch Run process. See Generate Index-Set Alternatives for more information.
  • To create your own virtual index sets that you can add to the list of SQL alternatives, click . See Add Your Own Virtual Index Sets for more information.


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