Union Operator

The UNION operator is used to combine the result-set of two or more SELECT statements, without repeating the duplicate records by default. Every SELECT statement within UNION must have the same number of columns or else SQL returns an error. The columns must also have similar data types. The columns in every SELECT statement must also be in the same order matching with their respective data types.

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

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

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

Note: The column names in the result-set are usually equal to the column names in the first SELECT statement.

1. WHERE clause and ORDER BY

SELECT column_name(s)
FROM table1
UNION ALL
SELECT column_name(s)
FROM table2
WHERE condition
ORDER BY column_name;