UNION

UNION combines the results of two or more SELECT statements into a single result set while removing duplicate rows.

Source data — Pattern 7: Set Operators

All queries run against the shared employees table (see schema.sql). This pattern introduces the former_employees table. Topic 44 also introduces a retired_employees table to demonstrate combining multiple set operators in a single query.

UNION — source table 1

UNION — source table 2

UNION — source table 3

What it does

UNION combines the results of two or more SELECT statements into a single result set while removing duplicate rows. Each SELECT statement must return the same number of columns in the same order with compatible data types.

Problem

Display the names of all current and former employees without duplicates.

SELECT first_name, last_name
FROM employees
UNION
SELECT first_name, last_name
FROM former_employees;

Result

UNION — result 4

SQL · Pattern 7 — Set Operators