Can you explain what the JOIN operator in SQL means and how it is used to combine tables?

The JOIN operator in SQL is used to combine rows from two or more tables based on a related column between them.

Main types of JOIN:

• INNER JOIN — returns only the rows where there are matches in both tables.
• LEFT JOIN (LEFT OUTER JOIN) — returns all rows from the left table and the matching rows from the right table; if there is no match, the right side will contain NULL.
• RIGHT JOIN (RIGHT OUTER JOIN) — the opposite, returns all rows from the right table and the matching rows from the left table.
• FULL JOIN (FULL OUTER JOIN) — returns all rows from both tables, filling with NULL where there are no matches.

Example:

SELECT employees.name, departments.name
FROM employees
JOIN departments ON employees.department_id = departments.id;

This query joins the employees and departments tables on the department_id field to get the employee's name and their department's name.