Poor Performance Of Native Full Outer Join (Doc ID 731209.1)

Last updated on SEPTEMBER 15, 2016

Applies to:

Oracle Server - Enterprise Edition - Version: 9.0.1.0 to 10.2.0.4
This problem can occur on any platform.

Symptoms

Performance of some queries using  native full outer join syntax available  since Oracle 9i version is slower for some queries compare with  the equivalent queries rewritten  as  UNION ALL of two separate subqueries,  i.e. without using full outer join syntax.  In some cases performance difference could be two and more  times.  

Cause

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