Explain different types of joins in SQL.

SQL joins combine rows from two or more tables based on a related column. The main types are:

1. INNER JOIN – returns rows where the join condition is true in both tables.
2. LEFT (OUTER) JOIN – returns all rows from the left table and matched rows from the right; unmatched right rows are NULL.
3. RIGHT (OUTER) JOIN – opposite of LEFT; all rows from the right table plus matched left rows.
4. FULL (OUTER) JOIN – returns rows when there is a match in either table; unmatched rows are NULL.
5. CROSS JOIN – returns the Cartesian product of the two tables.
6. SELF JOIN – a table joined to itself, useful for hierarchical data.

Choosing the right join depends on the desired result set and data relationships.