What are the types of joins in SQL?

In SQL, joins combine rows from two or more tables based on a related column. The most common join types are:

1. INNER JOIN – Returns only rows that have matching values in both tables. It’s the default join when you just write JOIN.
2. LEFT (OUTER) JOIN – Returns all rows from the left table and the matched rows from the right table. If there’s no match, the right side columns are NULL.
3. RIGHT (OUTER) JOIN – Opposite of LEFT JOIN; returns all rows from the right table and matched rows from the left.
4. FULL (OUTER) JOIN – Combines LEFT and RIGHT joins; returns all rows when there’s a match in either table, filling missing side with NULL.
5. CROSS JOIN – Produces the Cartesian product of two tables, returning every combination of rows.
6. SELF JOIN – A table joined to itself, useful for hierarchical or relational data within the same table.

Each join type serves different scenarios: INNER JOIN for filtering common data, OUTER joins for preserving data from one side, CROSS JOIN for generating combinations, and SELF JOIN for intra-table relationships. Understanding when to use each ensures efficient queries and accurate results.