SQL JOIN Visualizer

INNER JOIN returns only rows where the join condition matches in BOTH tables. LEFT JOIN (LEFT OUTER JOIN) returns all rows from the left table plus matched rows from the right table — unmatched right-side columns are NULL. Use LEFT JOIN when you want to keep all left-table rows regardless of whether there's a match.

CROSS JOIN produces the Cartesian product — every row from the left table paired with every row from the right table. A 5-row table CROSS JOINed with a 4-row table produces 20 rows. Usually accidental (missing ON clause); intentional uses include generating test data or combinations.

A SELF JOIN joins a table with itself, using table aliases. Common use cases: employee-manager hierarchies, finding duplicate rows, comparing rows within the same table. Example: SELECT e.name, m.name AS manager FROM employees e JOIN employees m ON e.manager_id = m.id.

FULL OUTER JOIN returns all rows from both tables, with NULLs where there's no match. Use it when you want to see non-matching rows from both sides — for example, finding records in Table A that have no match in Table B AND records in Table B with no match in Table A simultaneously.