SQL UNION Operator

            

UNION Operator:

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

Every SELECT statement within UNION must have the same number of columns

The columns must also have similar data types

The columns in every SELECT statement must also be in the same order

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

UNION ALL Operator:

The UNION operator selects only distinct values by default. To allow duplicate values, use UNION ALL operator.

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

SQL UNION With WHERE:

     SELECT City, Country FROM Customers WHERE Country='Germany'       UNION SELECT City, Country FROM Suppliers      WHERE Country='Germany' ORDER BY City;

This statement returns the German cities (only distinct values) from both the "Customers" and the "Suppliers" table: