Oracle Consulting Oracle Training Oracle Support Development
Home
Catalog
Oracle Books
SQL Server Books
IT Books
Job Interview Books
eBooks
Rampant Horse Books
911 Series
Pedagogue Books

Oracle Software
image
Write for Rampant
Publish with Rampant
Rampant News
Rampant Authors
Rampant Staff
 Phone
 800-766-1884
Oracle News
Oracle Forum
Oracle Tips
Articles by our Authors
Press Releases
SQL Server Books
image
image

Oracle 11g Books

Oracle tuning

Oracle training

Oracle support

Remote Oracle

STATSPACK Viewer

Privacy Policy

 

   
  SQL Server Tips by Burleson

Derived table

A derived table is a select statement inside parenthesis, with an alias, used as a table in a join or union. Derived tables are very common with JOIN clauses because they have a defined name, which is necessary for the join, unlike subqueries. They are an alternative to temporary tables in the same situations as subqueries. Another use for derived tables is in row calculations, particularly when there are excessive aggregate functions and CASE statements.

Example: same as the previous one.

SELECT TOP 100 PERCENT dbo.titles.title, dbo.titles.royalty
FROM dbo.titles
INNER JOIN
(SELECT (min(royalty)+max(royalty))/2 as avgTotal FROM dbo.roysched ) r2
on dbo.titles.royalty> avgTotal
ORDER BY dbo.titles.title

This is an example where the JOIN clause allows you to remove the WHERE clause to filter rows. Usually it is better to use a JOIN to filter rather than a WHERE statement but, in this case, both queries are at the same performance level.


The above book excerpt is from:

Super SQL Server Systems
Turbocharge Database Performance with C++ External Procedures

ISBN: 0-9761573-2-2
Joseph Gama, P. J. Naughter

 http://www.rampant-books.com/book_2005_2_sql_server_external_procedures.htm  

Linux Oracle commands syntax poster

ION Oracle tuning software

Oracle data dictionary reference poster



Oracle Forum

BC Oracle consulting support training

BC remote Oracle DBA   

 

   

 Copyright © 1996 -2016 by Burleson. All rights reserved.


Oracle® is the registered trademark of Oracle Corporation. SQL Server® is the registered trademark of Microsoft Corporation. 
Many of the designations used by computer vendors to distinguish their products are claimed as Trademarks
 

Hit Counter