In SQL, joins are used to combine rows from two or more tables based on a related column. The common types of joins are: INNER JOIN: Returns records that have matching values in both tables. Example: SELECT * FROM TableA INNER JOIN TableB ON TableA.id = TableB.id LEFT JOIN (or LEFT OUTER JOIN): Returns all records from the left table, and the matched records from the right table. Unmatched rows from the right table will have NULL values. Example: SELECT * FROM TableA LEFT JOIN TableB ON TableA.id = TableB.id RIGHT JOIN (or RIGHT OUTER JOIN): Returns all records from the right table, and the matched records from the left table. Unmatched rows from the left table will have NULL values. Example: SELECT * FROM TableA RIGHT JOIN TableB ON TableA.id = TableB.id FULL JOIN (or FULL OUTER JOIN): Returns all records when there is a match in either the left or right table. Unmatched rows from both tables will have NULL values. Example: SELECT * FROM TableA FULL JOIN TableB ON TableA.id = TableB.id CROSS JOIN: Returns the Cartesian product of the two tables, meaning every row in the first table is combined with every row in the second table. Example: SELECT * FROM TableA CROSS JOIN TableB SELF JOIN: A table is joined with itself to compare rows within the same table. Example: SELECT A.*, B.* FROM TableA A, TableA B WHERE A.id = B.parent_id