What is the purpose of the JOIN operator in SQL and what scenarios are there for its use?

The JOIN operator in SQL is used to combine rows from two or more tables based on a related column between them (usually a key). This allows you to retrieve combined data from different tables in a single query.

Main scenarios for using JOIN:

• INNER JOIN — returns only those records that have matches in both tables.
• LEFT JOIN (LEFT OUTER JOIN) — returns all records from the left table and matching records from the right table; if there are no matches, NULLs are returned for columns from the right table.
• RIGHT JOIN (RIGHT OUTER JOIN) — returns all records from the right table and matching records from the left table; if there are no matches, NULLs are returned for columns from the left table.
• FULL JOIN (FULL OUTER JOIN) — returns all records from both tables; where there are no matches, NULLs are used.

Example:

SELECT orders.id, customers.name
FROM orders
JOIN customers ON orders.customer_id = customers.id;

This query joins the orders and customers tables to get the customer name for each order.