SQL UNION Operator
The SQL UNION Operator
The 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 returns the cities (only distinct values) from both the "Customers" and the "Suppliers" table:
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 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;
Try it Yourself »
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;
Try it Yourself »
SQL UNION ALL With WHERE
The following SQL statement returns the German cities (duplicate values also) 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;
Try it Yourself »
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;
Try it Yourself »
Notice the "AS Type" above - it is an alias. SQL Aliases are used to give a table or a column a temporary name. An alias only exists for the duration of the query. So, here we have created a temporary column named "Type", that list whether the contact person is a "Customer" or a "Supplier".
