Poor Performance for Query with ROWNUM predicate and NESTED LOOPS.
(Doc ID 551749.1)
Last updated on FEBRUARY 20, 2019
Applies to:Oracle Database - Enterprise Edition - Version 126.96.36.199 to 188.8.131.52 [Release 11.1]
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Information in this document applies to any platform.
- Queries which include a ROWNUM predicate may get a suboptimal plan, typically including an expensive NESTED LOOPS join.
- Explain plan shows a join to a subquery or view which has incorrectly assumed that the cardinality returned will be that of the rownum predicate.
- Users might see a nested loop join in the plan when the query has a rownum predicate and contains a view.
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