Topic: Performance & Tuning >> Query Rewrite
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| rsreddy28 |
Posted: Mar 17, 2007 03:47:44 AM |
Total Post: 36
Joined: Mar, 2007
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Hello,
Can somebody tell me what is Query Rewrite. I got this question in an interview. I just told that it is used to improve the performance of queries by avoiding repeated statements.
Plz help me giving out what exactly happens inside with Query Rewrite and also the detailed script and how is it and where is it used.
Regards,
Rajasekhar Reddy |
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 naren |
| Posted: Mar 17, 2007 05:02:25 PM |  |
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Total Post: 6
Joined: Mar, 2007
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Hello...
When a query executes, the optimizer decides whether it is faster to access the materialized view or the underlying tables where the data resides. If the optimizer decides that querying the materialized view is the better solution, the optimizer rewrites the SQL query in a process known as query rewrite. This process occurs without requiring a change to any SQL or application code, so any application or ad hoc query tool that uses SQL to access the database can benefit by using the materialized view. Query rewrite works best where the amount of data accessed to compute the result is significantly greater than the size of the result, such as aggregation; however, it can also be used to speed up expensive joins or projections.
regards
-naren
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