Solved

Building a view with union

Posted on 2004-09-01
4
1,331 Views
Last Modified: 2007-12-19
Hi everybody:

I need to build a view in Oracle 8i or 9i. This view must make a UNION from to tables.

Example:

I have this:

table: employee
name: varchar
age: number

table: app_user
name: varchar
age: number

I need this:

create view myuser as
  select name, age from employee
     union
  select name, age from app_user

Thanks in advanced
0
Comment
Question by:vcarballo
4 Comments
 
LVL 12

Expert Comment

by:geotiger
ID: 11960210

I do not know why you are asking the question while you are providing the anwser at the same time. Have you tried yours? It should work:

CREATE OR REPLACE VIEW your_user_vw AS
SELECT name, age FROM employee
UNION
SELECT name,age FROM app_user;

GT

0
 

Expert Comment

by:sfardin
ID: 11960976
I agree with geotiger.  you have already answered your query.

Are you getting any error while creating view?
0
 
LVL 11

Accepted Solution

by:
cjjclifford earned 250 total points
ID: 11961424
Note that if you don't mind duplicates in the view (i.e. if there are possibly the same rows in both the "employee" and "app_user" tables, and these both occurring in the view), then use "UNION ALL" rather than "UNION" - UNION is a strict union, so any row in the resulting view will only appear once - to do this the UNION performs a full sort and filters any duplicate rows. UNION ALL is all the rows from the first SELECT and all the rows from the second SELECT, any duplicated rows will remain duplicates, but there is no sort etc... (basically, UNION with large tables is very unadvised, if at all possible to avoid... its very similar to using DISTINCT without needing it...

Cheers,
C.
0
 
LVL 1

Expert Comment

by:StevenTaylor
ID: 11961441
One thing to be aware of is that the UNION option will cause any identical entries in both tables to be only displayed once (which is probably what you want).  However, these are really big tables, remember that there will be a unique sort possibly causing a large performance overhead.

UNION ALL will simply join the results from both tables without the unique sort but this is only useful if each table stores different entries.
0

Featured Post

Announcing the Most Valuable Experts of 2016

MVEs are more concerned with the satisfaction of those they help than with the considerable points they can earn. They are the types of people you feel privileged to call colleagues. Join us in honoring this amazing group of Experts.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Article by: Swadhin
From the Oracle SQL Reference (http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/queries006.htm) we are told that a join is a query that combines rows from two or more tables, views, or materialized views. This article provides a glimps…
Working with Network Access Control Lists in Oracle 11g (part 1) Part 2: http://www.e-e.com/A_9074.html So, you upgraded to a shiny new 11g database and all of a sudden every program that used UTL_MAIL, UTL_SMTP, UTL_TCP, UTL_HTTP or any oth…
This video shows how to Export data from an Oracle database using the Original Export Utility.  The corresponding Import utility, which works the same way is referenced, but not demonstrated.
This video shows how to configure and send email from and Oracle database using both UTL_SMTP and UTL_MAIL, as well as comparing UTL_SMTP to a manual SMTP conversation with a mail server.

813 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

13 Experts available now in Live!

Get 1:1 Help Now