What is the difference between JOIN and UNION?

JOIN combines rows from two or more tables based on a related column between them. UNION combines the result sets of two or more SELECT queries into a single result set.

Key differences:

Characteristic	JOIN	UNION
Purpose	Combining columns from different tables	Combining rows from different result sets
Requirements	Presence of a common column for joining	Same number of columns and compatible data types in SELECT queries
Types	INNER, LEFT, RIGHT, FULL	UNION (removes duplicates), UNION ALL (keeps duplicates)

Example of JOIN (SQL):

SELECT
    Customers.CustomerName,
    Orders.OrderID
FROM
    Customers
INNER JOIN
    Orders ON Customers.CustomerID = Orders.CustomerID;

Example of UNION (SQL):

SELECT City FROM Customers
UNION
SELECT City FROM Suppliers;