MySQL UNION

The MySQL UNION Operator

The UNION operator in MySQL combines the result sets of two or more SELECT statements.

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

UNION Syntax

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

UNION ALL Syntax

By default, the UNION operator selects only distinct values. To include duplicate values, use UNION ALL instead.

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

Note: The column names in the result set typically match the column names in the first SELECT statement.

Demo Database

In this tutorial, we’ll be working with the well-known Northwind sample database.

Here is a portion of 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 here is a portion of 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 retrieves the distinct cities from both the “Customers” and the “Suppliers” tables:

Example

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

Note: If some customers or suppliers share the same city, each city will appear only once in the result because UNION selects only distinct values. To include duplicate values, use UNION ALL instead.

SQL UNION ALL Example

The following SQL statement retrieves the cities, including duplicate values, from both the “Customers” and the “Suppliers” table:

Example

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

SQL UNION With WHERE

The following SQL statement retrieves distinct German cities from both the “Customers” and the “Suppliers” tables:

Example

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

SQL UNION ALL With WHERE

The following SQL statement retrieves German cities, including duplicate values, from both the “Customers” and the “Suppliers” table:

Example

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

Another UNION Example

The following SQL statement combines all customers and suppliers:

Example

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

Notice the “AS Type” above – it serves as an alias. SQL aliases provide temporary names to tables or columns within a query. An alias exists only for the duration of the query. In this case, we’ve created a temporary column named “Type” to indicate whether the contact person is a “Customer” or a “Supplier”.