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Oracle DB Query timeout when using Group By clause

edited Jun 23, 2016 7:21PM in SQL Performance (MOSC) 27 commentsAnswered

I have a comprehensive SQL with many nesting Subqueries. At the end on nesting sqls I use Group By statement.

The query can not run (take very log time untill timeout).

However when I remove group by statement, query can return 500k rows in several minutes.

Execution plan shows that it takes 76% CPU time on HASH GROUP BY and 16% CPU time on HASH JOIN RIGHT OUTER.

Please help to solve the problem.


It should be an execution optimazation problem of Oracle DB.

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