| student_id | course | |------------|-----------| | 1 | Math | | 2 | Science | | 4 | Art | Returns only rows with matching keys in BOTH tables.
SELECT * FROM students CROSS JOIN courses; Result: 3 × 3 = 9 rows. A table joined with itself. Useful for hierarchical data (e.g., employee-manager).
📊 Intersection of A and B. 3.2 LEFT JOIN (or LEFT OUTER JOIN) Returns ALL rows from the left table, matched rows from the right table. NULL if no match.
SELECT e.name, d.dept_name FROM employees e JOIN departments d ON e.dept_id = d.dept_id; Assume two tables:
| student_id | course | |------------|-----------| | 1 | Math | | 2 | Science | | 4 | Art | Returns only rows with matching keys in BOTH tables.
SELECT * FROM students CROSS JOIN courses; Result: 3 × 3 = 9 rows. A table joined with itself. Useful for hierarchical data (e.g., employee-manager). sql joins notes pdf
📊 Intersection of A and B. 3.2 LEFT JOIN (or LEFT OUTER JOIN) Returns ALL rows from the left table, matched rows from the right table. NULL if no match. | student_id | course | |------------|-----------| | 1
SELECT e.name, d.dept_name FROM employees e JOIN departments d ON e.dept_id = d.dept_id; Assume two tables: Assume two tables: