The SQL UNION operator combines two or more SELECT statements.
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.
Note: The UNION operator selects only distinct values by default. To allow duplicate values, use UNION ALL.
PS: The column names in the result-set of a UNION are always equal to the column names in the first SELECT statement in the UNION.
In this tutorial we will use the well-known Northwind sample database.
Below is a selection from the "Customers" table:
||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:
|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|
The following SQL statement selects all the different cities from the "Customers" and "Suppliers" tables:
Note: This command cannot be used to list all cities from the two tables. In the example above several customers and suppliers share the same city, but each city will only be listed once. The UNION command selects only distinct values.
The following SQL statement selects all the cities from the "Customers" and "Suppliers" tables:
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