SQL UNION Operator

SQL

SQL UNION Operator : SQL UNION Operator is used to combine the result-set of two or more SELECT statements.

  • Each SELECT statement within UNION must have the same number of columns
  • The columns must also have similar data types
  • The columns in each SELECT statement must also be in the same order

UNION Syntax

SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2;

UNION ALL Syntax

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

SELECT column_name(s) FROM table1
UNION ALL
SELECT column_name(s) FROM table2;

Note:

The column names in the result-set are usually equal to the column names in the first SELECT statement in the UNION.

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the “Customers” table:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

And a selection from the “Suppliers” table:

SupplierID SupplierName ContactName Address City PostalCode Country
1 Exotic Liquid Charlotte Cooper 49 Gilbert St. London EC1 4SD UK
2 New Orleans Cajun Delights Shelley Burke P.O. Box 78934 New Orleans 70117 USA
3 Grandma Kelly’s Homestead Regina Murphy 707 Oxford Rd. Ann Arbor 48104 USA

SQL UNION Example

The following SQL statement selects all the different cities (only distinct values) from “Customers” and “Suppliers”:

Example

SELECT City FROM Customers
UNION
SELECT City FROM Suppliers
ORDER BY City;

 

Output

Number of Records: 7

City
Aachen
Albuquerque
Anchorage
Ann Arbor
Annecy
Barcelona
Barquisimeto
Bend

 

Note:

If some customers or suppliers have the same city, each city will only be listed once, because UNION selects only distinct values. Use UNION ALL to also select duplicate values!

SQL UNION ALL Example

The following SQL statement selects all cities (duplicate values also) from “Customers” and “Suppliers”:

Example

SELECT City FROM Customers
UNION ALL
SELECT City FROM Suppliers
ORDER BY City;

 

Output

Number of Records: 7

City
Aachen
Albuquerque
Anchorage
Ann Arbor
Annecy
Barcelona
Barquisimeto

 

SQL UNION With WHERE

The following SQL statement selects all the different German cities (only distinct values) from “Customers” and “Suppliers”:

Example

SELECT City, Country FROM Customers
WHERE Country=’Germany’
UNION
SELECT City, Country FROM Suppliers
WHERE Country=’Germany’
ORDER BY City;

 

Output

Number of Records: 13

City Country
Aachen Germany
Berlin Germany
Brandenburg Germany
Cunewalde Germany
Cuxhaven Germany
Frankfurt Germany
Frankfurt a.M. Germany
Köln Germany
Leipzig Germany
Mannheim Germany
München Germany
Münster Germany
Stuttgart Germany

 

SQL UNION ALL With WHERE

The following SQL statement selects all German cities (duplicate values also) from “Customers” and “Suppliers”:

Example

SELECT City, Country FROM Customers
WHERE Country=’Germany’
UNION ALL
SELECT City, Country FROM Suppliers
WHERE Country=’Germany’
ORDER BY City;

 

Output

Number of Records: 14

City Country
Aachen Germany
Berlin Germany
Berlin Germany
Brandenburg Germany
Cunewalde Germany
Cuxhaven Germany
Frankfurt Germany
Frankfurt a.M. Germany
Köln Germany
Leipzig Germany
Mannheim Germany
München Germany
Münster Germany
Stuttgart Germany

Another UNION Example

The following SQL statement lists all customers and suppliers:

Example

SELECT ‘Customer’ As Type, ContactName, City, Country
FROM Customers
UNION
SELECT ‘Supplier’, ContactName, City, Country
FROM Suppliers;

 

Output

Number of Records: 6

Type ContactName City Country
Customer Alejandra Camino Madrid Spain
Customer Alexander Feuer Leipzig Germany
Customer Ana Trujillo México D.F. Mexico
Customer Anabela Domingues São Paulo Brazil
Customer André Fonseca Campinas Brazil
Customer Ann Devon London UK