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

 
 Home
 E-mail Us
 Oracle Articles


 Oracle Training
 Oracle Tips

 Oracle Forum
 Class Catalog


 Remote DBA
 Oracle Tuning
 Emergency 911
 RAC Support
 Apps Support
 Analysis
 Design
 Implementation
 Oracle Support


 SQL Tuning
 Security

 Oracle UNIX
 Oracle Linux
 Monitoring
 Remote s
upport
 Remote plans
 Remote
services
 Application Server

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

 Remote S
upport  
 Development  

 Implementation


 Consulting Staff
 Consulting Prices
 Help Wanted!

 


 Oracle Posters
 Oracle Books

 Oracle Scripts
 Ion
 Excel-DB  

Don Burleson Blog 


 

 

 


 

 

 
 

Oracle Inline views

Oracle Tips by Burleson Consulting
Don Burleson


Question:  What is an Oracle "in-line view?  How do I use an inline view?

Answer:  The inline view is a construct in Oracle SQL where you can place a query in the SQL FROM, clause, just as if the query was a table name.

Oracle has long supported the notion of an 'in-line view,' whereby a subquery can be placed in the FROM clause, just as if it were a table name. There's an Oracle query displaying tablespace sizes:

A common use for in-line views in Oracle SQL is to simplify complex queries by removing join operations and condensing several separate queries into a single query.

The best example of the in-line view is the common Oracle DBA script that is used to show the amount of free space and used space within all Oracle tablespaces. Let?s take a close look at this SQL to see how it works. Carefully note that the FROM clause in this SQL query specifies two sub-queries that perform summations and grouping from two views, dba_data_files, and dba_free_space.

In ANSI standard SQL, it is quite difficult to compare two result sets that are summed together in a single query, and this is a common problem with Oracle SQL where specific values must be compared to a summary.  Without the use of an in-line view, several separate SQL queries would need to be written, one to compute the sums from each view and another to compare the intermediate result sets.

This is a great report for display the actual amount of free space within an Oracle tablespace.

column "Tablespace" format a13
column "Used MB"    format 99,999,999
column "Free MB"    format 99,999,999
colimn "Total MB"   format 99,999,999

select
   fs.tablespace_name                          "Tablespace",
   (df.totalspace - fs.freespace)              "Used MB",
   fs.freespace                                "Free MB",
   df.totalspace                               "Total MB",
   round(100 * (fs.freespace / df.totalspace)) "Pct. Free"
from
   (select
      tablespace_name,
      round(sum(bytes) / 1048576) TotalSpace
   from
      dba_data_files
   group by
      tablespace_name
   ) df,
   (select
      tablespace_name,
      round(sum(bytes) / 1048576) FreeSpace
   from
      dba_free_space
   group by
      tablespace_name
   ) fs
where
   df.tablespace_name = fs.tablespace_name;

This SQL quickly compares the sum of the total space within each tablespace to the sum of the free space within each tablespace. Here is a sample of the output:

Basically, this query needs to compare the sum of total space within each tablespace with the sum of the free space within each tablespace.


Here is the output from this in-line view query against the data dictionary.
Tablespace    Block Size     Used MB     Free MB    Total MB  Pct. Free        
------------- ---------- ----------- ----------- ----------- ----------        
CWMLITE            4,096           6          14          20         70        
DRSYS              4,096           8          12          20         60        
EXAMPLE            4,096         153           0         153          0        
INDX               4,096           0          25          25        100        
SYSTEM             4,096         241          84         325         26        
TOOLS              4,096           7           3          10         30        
TS_16K            16,384           3           7          10         70        
UNDOTBS            4,096           1         199         200        100        


In the simple example, the SQL subqueries are placed inside the FROM clause and assigned the aliases of df and fs. The df and fs subquery values are then referenced inside the SELECT clause. If you examine this query, you'll see that it sums and compares two ranges of values from two tables, all in a single query.

For some readers, seeing SQL inside the FROM clause is probably quite strange, and the scalar subquery is even stranger! The scalar subquery is a take-off of the in-line view whereby SQL subqueries can be placed inside the SELECT clause. Let's take a look at a few examples.

 
 
 
Get Complete Oracle Tuning Details 

The landmark book "Oracle Tuning: The Definitive Reference Third Edition" has been updated with over 800 pages of expert performance tuning tips. It's packed with scripts and tools to hypercharge Oracle performance and you can buy it for 40% off directly from the publisher.
 

 


 

 

��  
 
 

 
 
 
 
oracle dba poster
 

 
 
Oracle performance tuning software 
 
Oracle Linux poster
 
 
 

 

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 -  2014

All rights reserved by Burleson

Oracle ? is the registered trademark of Oracle Corporation.