How many rows will LEFT JOIN, RIGHT JOIN, and INNER JOIN return for tables of 3 and 5 rows?

Let's consider two tables: the first with 3 rows, and the second with 5 rows.

• INNER JOIN will return only those rows that have matches based on the join condition. The maximum number of rows is the number of matching pairs. Without a specific condition, it's not possible to say exactly, but usually, this is ≤ min(3,5).

• LEFT JOIN will return all 3 rows from the left table, supplemented with matching rows from the right table. If there are no matches, the fields from the right table will be NULL. The number of rows will be at least 3.

• RIGHT JOIN will return all 5 rows from the right table, supplemented with matching rows from the left table. If there are no matches, the fields from the left table will be NULL. The number of rows will be at least 5.

Example:

-- Table A (3 rows): 1,2,3
-- Table B (5 rows): 2,3,4,5,6

SELECT * FROM A INNER JOIN B ON A.id = B.id; -- returns rows with id 2 and 3 (2 rows)
SELECT * FROM A LEFT JOIN B ON A.id = B.id; -- returns 3 rows: for id 1 with NULL on the right, for 2 and 3 with matches
SELECT * FROM A RIGHT JOIN B ON A.id = B.id; -- returns 5 rows: for 4,5,6 with NULL on the left, for 2 and 3 with matches

Thus, the number of rows depends on the matches based on the join condition.