w3schools    w3Schools
Search W3Schools :
   
HOME HTML CSS XML JAVASCRIPT ASP PHP SQL MORE...   References Examples Forum About
ADVERTISEMENTS

XML Certification
Download XML editor
Custom Programming
 
Table of contents
SQL Basic
SQL HOME
SQL Intro
SQL Syntax
SQL Select
SQL Distinct
SQL Where
SQL And & Or
SQL Order By
SQL Insert
SQL Update
SQL Delete

SQL Demo
SQL Try It

SQL Advanced
SQL Top
SQL Like
SQL Wildcards
SQL In
SQL Between
SQL Alias
SQL Joins
SQL Inner Join
SQL Left Join
SQL Right Join
SQL Full Join
SQL Union
SQL Select Into
SQL Create DB
SQL Create Table
SQL Constraints
SQL Not Null
SQL Unique
SQL Primary Key
SQL Foreign Key
SQL Check
SQL Default
SQL Create Index
SQL Drop
SQL Alter
SQL Increment
SQL Views
SQL Dates
SQL Nulls
SQL isnull()
SQL Data Types

SQL Functions
SQL Functions
SQL avg()
SQL count()
SQL first()
SQL last()
SQL max()
SQL min()
SQL sum()
SQL Group By
SQL Having
SQL ucase()
SQL lcase()
SQL mid()
SQL len()
SQL round()
SQL now()
SQL format()

SQL Quick Ref
SQL Hosting
SQL Summary

SQL Quiz
SQL Quiz

Selected Reading
Web Statistics
Web Glossary
Web Hosting
Web Quality

W3Schools Tutorials
W3Schools Forum

Helping W3Schools

 

SQL UNION Operator

previous next

The SQL UNION operator combines two or more SELECT statements.


The SQL UNION Operator

The UNION operator is used to combine the result-set of two or more SELECT statements.

Notice that each SELECT statement within the UNION must have the same number of columns. The columns must also have similar data types. Also, the columns in each SELECT statement must be in the same order.

SQL UNION Syntax

SELECT column_name(s) FROM table_name1
UNION
SELECT column_name(s) FROM table_name2

Note: The UNION operator selects only distinct values by default. To allow duplicate values, use UNION ALL.

SQL UNION ALL Syntax

SELECT column_name(s) FROM table_name1
UNION ALL
SELECT column_name(s) FROM table_name2

PS: The column names in the result-set of a UNION are always equal to the column names in the first SELECT statement in the UNION.


SQL UNION Example

Look at the following tables:

"Employees_Norway":

E_ID E_Name
01 Hansen, Ola
02 Svendson, Tove
03 Svendson, Stephen
04 Pettersen, Kari

"Employees_USA":

E_ID E_Name
01 Turner, Sally
02 Kent, Clark
03 Svendson, Stephen
04 Scott, Stephen

Now we want to list all the different employees in Norway and USA.

We use the following SELECT statement:

SELECT E_Name FROM Employees_Norway
UNION
SELECT E_Name FROM Employees_USA

The result-set will look like this:

E_Name
Hansen, Ola
Svendson, Tove
Svendson, Stephen
Pettersen, Kari
Turner, Sally
Kent, Clark
Scott, Stephen

Note: This command cannot be used to list all employees in Norway and USA. In the example above we have two employees with equal names, and only one of them will be listed. The UNION command selects only distinct values.


SQL UNION ALL Example

Now we want to list all employees in Norway and USA:

SELECT E_Name FROM Employees_Norway
UNION ALL
SELECT E_Name FROM Employees_USA

Result

E_Name
Hansen, Ola
Svendson, Tove
Svendson, Stephen
Pettersen, Kari
Turner, Sally
Kent, Clark
Svendson, Stephen
Scott, Stephen


previous next


Learn XML with <oXygen/> XML Editor - Free Trial!

oXygen - Probably The World's Best XML Editor   

oXygen helps you learn to define, edit, validate and transform XML documents. Supported technologies include XML Schema, DTD, Relax NG, XSLT, XPath, XQuery, CSS.

Understand in no time how XSLT and XQuery work by using the intuitive oXygen debugger!

Do you have any XML related questions? Get free answers from the oXygen XML forum and from the video demonstrations.

Download a FREE 30-day trial today!


 
WEB HOSTING
Name Registration
Domain Name
Registration & More!
$15 Domain Name
Registration
Save $20 / year!
Buy UK Domain Names
Register Domain Names
Cheap Domain Names
Cheap Web Hosting
Best Web Hosting
PHP MySQL Hosting
Top 10 Web Hosting
UK Reseller Hosting
Web Hosting
FREE Web Hosting
WEB BUILDING
Website Templates
Flash Templates
Website Builder
Internet Business Opportunity
Custom Programming
FREE Trial or Demo
Web Content Manager
Forms,Web Alerts,RSS
Download XML editor
FREE Flash Website
FREE Web Templates
EDUCATION
US Web Design Schools
HTML Certification
JavaScript Certification
XML Certification
PHP Certification
ASP Certification

Home HOME or Top of Page Validate   Validate   W3C-WAI level A conformance icon Printer Friendly  Printer Friendly

W3Schools is for training only. We do not warrant the correctness of its content. The risk from using it lies entirely with the user.
While using this site, you agree to have read and accepted our terms of use and privacy policy.
Copyright 1999-2009 by Refsnes Data. All Rights Reserved.