SQL - UNION & UNION ALL

Overview

UNION removes duplicates across queries; UNION ALL preserves duplicates.

SELECT first_name AS name FROM employees
UNION
SELECT name FROM customers;

SELECT first_name AS name FROM employees
UNION
SELECT name FROM customers;

SELECT first_name AS name FROM employees
UNION
SELECT name FROM customers;

Prerequisite

Load the Standard Test Data.

Expected Output (live)

Sample Use Cases (2)

1) UNION ALL (Compare row counts)

2) Distinct cities across employees + customers