QUERY_REWRITE_ENABLED
时间：2014-05-11 07:08:00
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QUERY_REWRITE_ENABLED
| Property | Description |
|---|---|
| Parameter type | String |
| Syntax | QUERY_REWRITE_ENABLED = { false | true | force } |
| Default value | If OPTIMIZER_FEATURES_ENABLE is set to 10.0.0 or higher, then true
If |
| Modifiable | ALTER SESSION, ALTER SYSTEM |
| Real Application Clusters | Multiple instances can have different values. |
QUERY_REWRITE_ENABLED allows you to enable or disable query rewriting globally for the database.
Values:
-
falseOracle does not use rewrite.
-
trueOracle costs the query with rewrite and without rewrite and chooses the method with the lower cost.
-
forceOracle always uses rewrite and does not evaluate the cost before doing so. Use
forcewhen you know that the query will always benefit from rewrite and when reduction in compile time is important.
To take advantage of query rewrite for a particular materialized view, you must enable query rewrite for that materialized view, and you must enable cost-based optimization.
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