SQL UNION and UNION ALL

UNION

The UNION command is used to select related information from two tables, much like the JOIN

command. However, when using the UNION command all selected columns need to be of the same

data type.

Note: With UNION, only distinct values are selected.

SQL Statement 1

UNION

SQL Statement 2

Employees_Norway:

Employees_USA:

Using the UNION Command

Example

List all different employee names in Norway and USA:

SELECT E_Name FROM Employees_Norway

UNION

SELECT E_Name FROM Employees_USA

Result

Note: This command cannot be used to list all employees in Norway and USA. In the example

above we have two employees with equal names, and only one of them is listed. The UNION

command only selects distinct value

UNION ALL

The UNION ALL command is equal to the UNION command, except that UNION ALL selects all values.

SQL Statement 1

UNION ALL

SQL Statement 2

Using the UNION ALL Command

Example

List all employees in Norway and USA:

SELECT E_Name FROM Employees_Norway

UNION ALL

SELECT E_Name FROM Employees_USA

Result