Call now: 252-767-6166  
Oracle Training Oracle Support Development Oracle Apps

 E-mail Us
 Oracle Articles
New Oracle Articles

 Oracle Training
 Oracle Tips

 Oracle Forum
 Class Catalog

 Remote DBA
 Oracle Tuning
 Emergency 911
 RAC Support
 Apps Support
 Oracle Support

 SQL Tuning

 Oracle UNIX
 Oracle Linux
 Remote s
 Remote plans
 Application Server

 Oracle Forms
 Oracle Portal
 App Upgrades
 SQL Server
 Oracle Concepts
 Software Support

 Remote S


 Consulting Staff
 Consulting Prices
 Help Wanted!


 Oracle Posters
 Oracle Books

 Oracle Scripts

Don Burleson Blog 







Oracle SQL Join Factorization Transformation (JFT) Tips

Expert Oracle Database Tips by Donald BurlesonMarch 15, 2015


The UNION operator is great for merging the results of multiple queries that return similar rowsets, essentially executing each query separately and merging the results together into a single result set. 

Oracle continues to improve the SQL optimizer with each new release and Oracle has improved how Oracle handles UNION ALL performance in Oracle 11g release 2 with the new join factorization transformation (JFT).  The Join Factorization Transformation applies only to UNION ALL queries.

The Oracle CBO Group gives this example on how the optimizer now improves the performance of UNION ALL by dynamically re-writing a UNION ALL query into a more efficient form using an in-line view:

    select t1.c1, t2.c2     
    from t1, t2, t3    
    where t1.c1 = t2.c1 and t1.c1 > 1 and t2.c2 = 2 and t2.c2 = t3.c2   
union all    
    select t1.c1, t2.c2    
    from t1, t2, t4    
    where t1.c1 = t2.c1 and t1.c1 > 1 and t2.c3 = t4.c3;

Table t1 appears in both the branches. As does the filter predicates on t1 (t1.c1 > 1) and the join predicates involving t1 (t1.c1 = t2.c1). Nevertheless, without any transformation, the scan (and the filtering) on t1 has to be done twice, once per branch. Such a query may benefit from join factorization which can transform Q1 into Q2 as follows:

     select t1.c1, VW_JF_1.item_2
     from t1, (select t2.c1 item_1, t2.c2 item_2
                    from t2, t3
                    where t2.c2 = t3.c2 and t2.c2 = 2
               union all
                    select t2.c1 item_1, t2.c2 item_2
                    from t2, t4
                    where t2.c3 = t4.c3) VW_JF_1
     where t1.c1 = VW_JF_1.item_1 and t1.c1 > 1;

In Q2, t1 is "factorized" and thus the table scan and the filtering on t1 is done only once (it's shared). If t1 is large, then avoiding one extra scan of t1 can lead to a huge performance improvement.

As we see the Join Factorization Transformation simply transforms simple UNION ALL queries into in-line views, thereby avoiding an extra full-table scan. Again, the Join Factorization Transformation query re-write is complete transparent, and you do not need to do anything at all to utilize this feature in Oracle 11gR2.

Get the Complete
Oracle SQL Tuning Information 

The landmark book "Advanced Oracle SQL Tuning  The Definitive Reference"  is filled with valuable information on Oracle SQL Tuning. This book includes scripts and tools to hypercharge Oracle 11g performance and you can buy it for 30% off directly from the publisher.



Burleson is the American Team

Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. All legitimate Oracle experts publish their Oracle qualifications.

Errata?  Oracle technology is changing and we strive to update our BC Oracle support information.  If you find an error or have a suggestion for improving our content, we would appreciate your feedback.  Just  e-mail:  

and include the URL for the page.


Burleson Consulting

The Oracle of Database Support

Oracle Performance Tuning

Remote DBA Services


Copyright © 1996 -  2020

All rights reserved by Burleson

Oracle ® is the registered trademark of Oracle Corporation.



Oracle Training at Sea
oracle dba poster

Follow us on Twitter 
Oracle performance tuning software 
Oracle Linux poster