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.

SQL UNION ALL Syntax

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

Note : The UNION operator selects All (duplicate values also) values by default.

SELECT City FROM Customer 
UNION 

SELECT City FROM Supplier 

ORDER BY City

  
 

 
Result:
 

SELECT City FROM Customer 
UNION 
SELECT City FROM Supplier 
ORDER BY City