SQL UNION Operator

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# SQL UNION Operator

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The SQL UNION operator combines the result of two or more SELECT statements.

## The SQL UNION Operator

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

Notice that each SELECT statement within the UNION must have the same number of columns. The columns must also have similar data types. Also, the columns in each SELECT statement must be in the same order.

### SQL UNION Syntax

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

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

### SQL UNION ALL Syntax

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

PS: The column names in the result-set of a UNION 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. | Londona | 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 the "Customers" and the "Suppliers" tables:

## Example

SELECT City FROM Customers
UNION
SELECT City FROM Suppliers
ORDER BY City;
Try it yourself »

Note: UNION cannot be used to list ALL cities from the two tables. If several customers and suppliers share the same city, each city will only be listed once. UNION selects only distinct values. Use UNION ALL to also select duplicate values!

## SQL UNION ALL Example

The following SQL statement uses UNION ALL to select all (duplicate values also) cities from the "Customers" and "Suppliers" tables:

## Example

SELECT City FROM Customers
UNION ALL
SELECT City FROM Suppliers
ORDER BY City;
Try it yourself »

## SQL UNION ALL With WHERE

The following SQL statement uses UNION ALL to select all (duplicate values also) German cities from the "Customers" and "Suppliers" tables:

## 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 »
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