How can you determine the features and types of JOIN operations in SQL queries?

SQL JOIN operations are used to combine rows from two or more tables based on a related condition.

Main types of JOIN:

• INNER JOIN — returns only the rows where there is a match in both tables.
• LEFT JOIN (LEFT OUTER JOIN) — returns all rows from the left table and the matching rows from the right; if there is no match, NULLs are used for the right table.
• RIGHT JOIN (RIGHT OUTER JOIN) — the opposite, returns all rows from the right table and the matching rows from the left.
• FULL JOIN (FULL OUTER JOIN) — returns all rows from both tables; where there is no match, NULLs are used.
• CROSS JOIN — Cartesian product of two tables, each row of the first table is combined with each row of the second.

Example of INNER JOIN:

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

This selects employee names and their department names only if the relationship exists.