SQL UNION Statement

SQL UNION Description

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

Each SELECT statement in UNION must have the same number of columns

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

The column names in the result set usually match the column names in the first SELECT statement.

Demonstration database

In this tutorial we will use the famous example database "Northwind".

Below is a sample from the table "Customers" ("Customers"):

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.	5021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	5023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

And the sample from the table "Suppliers" ("Suppliers"):

SupplierID	SupplierName	ContactName	Address	City	PostalCode	Country	Phone
1	Exotic Liquid	Charlotte Cooper	49 Gilbert St.	Londona	EC1 4SD	UK	(171) 555-2222
2	New Orleans Cajun Delights	Shelley Burke	P.O. Box 78934	New Orleans	70117	USA	(100) 555-4822
3	Grandma Kelly's Homestead	Regina Murphy	707 Oxford Rd.	Ann Arbor	48104	USA	(313) 555-5735
4	Tokyo Traders	Yoshi Nagase	9-8 Sekimai Musashino-shi	Tokyo	100	Japan	(03) 3555-5011
5	Cooperativa de Quesos 'Las Cabras'	Antonio del Valle Saavedra	Calle del Rosal 4	Oviedo	33007	Spain	(98) 598 76 54

SQL UNION Example

The following SQL statement selects cities (different values only) from the Customers and Suppliers tables:

Run SQLSELECT City FROM Customers 
UNION 
SELECT City FROM Suppliers 
ORDER BY City

If some customers or suppliers have the same city (City), each city will be specified only once because UNION only selects different values. Use UNION ALL to select duplicate values too!

SQL UNION ALL Example

The following SQL statement selects cities (also duplicate values) from both the Customers and Suppliers tables:

Run SQLSELECT City FROM Customers 
UNION ALL 
SELECT City FROM Suppliers 
ORDER BY City

SQL UNION together with WHERE

The following SQL statement selects German cities (different values only) from both the Customers and Suppliers tables:

Run SQLSELECT City, Country FROM Customers 
WHERE Country = 'Germany' 
UNION 
SELECT City, Country FROM Suppliers 
WHERE Country = 'Germany' 
ORDER BY City

SQL UNION ALL together with WHERE

The following SQL statement selects German cities (also duplicate values) from both the Customers and Suppliers tables:

Run SQLSELECT City, Country FROM Customers 
WHERE Country = 'Germany' 
UNION ALL 
SELECT City, Country FROM Suppliers 
WHERE Country = 'Germany' 
ORDER BY City

Another SQL UNION Example

The following SQL statement lists all customers and suppliers:

Run SQLSELECT 'Customer' AS Type, ContactName, City, Country 
FROM Customers 
UNION 
SELECT 'Supplier', ContactName, City, Country 
FROM Suppliers

Note the "AS Type" above is an alias. SQL aliases are used to give a table or column a temporary name. The alias exists only for the duration of the request. So, here we have created a temporary column called "Type" that indicates whether the contact is a "Customer" or a "Vendor".