MySQL UNION Operator

              MySQL UNION Operator

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

• Every SELECT statement within UNION must have the same number of columns
• The columns must also have similar data types
• The columns in every 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 UNIONoperator 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;

Demo Database

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

Below is a selection from the “Customers” table:

Customers

And a selection from the “Suppliers” table:

Suppliers

SQL UNION Example

The following SQL statement returns the cities (only distinct values) from both the “Customers” and the “Suppliers” table:

Example

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

SQL UNION ALL Example

The following SQL statement returns the cities (duplicate values also) 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 returns the German cities (only distinct values) from both the “Customers” and the “Suppliers” table:

Example

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

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;