CROSS JOIN

Produces the Cartesian product — every row in the left table is paired with every row in the right table. There is no ON condition. With 4 employees and 3 departments, the result is 4 × 3 = 12 rows.

SELECT e.name, d.dept_name
FROM employees e
CROSS JOIN departments d;

rows_in_A × rows_in_B = output rows

Warning: On large tables, CROSS JOINs are extremely expensive. A table of 1,000 rows crossed with another 1,000-row table yields 1,000,000 rows.

• Generating all possible combinations (e.g., size × color for product variants)
• Creating test data
• Building a calendar — cross joining a list of dates with a list of time slots