Solved

Unions for Dummies

Posted on 2011-03-10
1
416 Views
Last Modified: 2012-05-11
I created a query that involved a bunch of joins.  Had a real SQL pro look at the query results and apparently they included too much.  The pro redid the query using a UNION.

Can someone explain to me what the data would look like in general for the pro to use a join?

What are the steps in deciding what select statements on each side of the join would look like?  I guess I'm asking for "how to do a union" explanation.
0
Comment
Question by:lcor
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
1 Comment
 
LVL 77

Accepted Solution

by:
slightwv (䄆 Netminder) earned 500 total points
ID: 35098594
The simple on a straight UNION.

Take the unique results from: Give me everything from queryA add it to the results of give me everything from queryB.

A "UNION ALL" doesn't take unique records.

The caveats:
The number of columns must match and the datatypes for each individual column across the multiple queries must match.

You can do:
select 'string1' col1 , to_number(1) col2 from dual
union
select 'string2' col1 , to_number(2) col2 from dual

You cannot do:

select 'string1' col1 , to_number(1) col2 from dual
union
select to_number(2) col1 , 'string2' col2 from dual

The data types don't match.
0

Featured Post

Major Incident Management Communications

Major incidents and IT service outages cost companies millions. Often the solution to minimizing damage is automated communication. Find out more in our Major Incident Management Communications infographic.

Question has a verified solution.

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

Suggested Solutions

Configuring and using Oracle Database Gateway for ODBC Introduction First, a brief summary of what a Database Gateway is.  A Gateway is a set of driver agents and configurations that allow an Oracle database to communicate with other platforms…
From implementing a password expiration date, to datatype conversions and file export options, these are some useful settings I've found in Jasper Server.
Via a live example, show how to take different types of Oracle backups using RMAN.
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.

739 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