What types of table joins exist in relational databases?

In relational databases, there are several main types of joins that allow combining data from two or more tables:

• INNER JOIN — returns only the records that have matches in both tables.
• LEFT JOIN (LEFT OUTER JOIN) — returns all records from the left table and the matching records from the right; if there are no matches, the right table fields will be NULL.
• RIGHT JOIN (RIGHT OUTER JOIN) — conversely, returns all records from the right table and the matching records from the left.
• FULL JOIN (FULL OUTER JOIN) — returns all records from both tables, filling with NULL where there are no matches.
• CROSS JOIN — the Cartesian product of two tables, returning all possible combinations of rows.

Example of INNER JOIN:

SELECT users.name, orders.id
FROM users
INNER JOIN orders ON users.id = orders.user_id;

This query will return users with their orders only if the user has an order.