A. Joins¶
1. inner¶
2. outer¶
- left outer
- right outer
3. Cross¶
- Results in m × n rows (where m and n are row counts of each table)
- every row from the first table is combined with every row from the second table
- No join condition is specified
self join¶
- special case: regular join (inner, outer, cross) where a table is joined with itself.
- it's useful for querying hierarchical data or comparing rows within the same table
- Commonly used eg:
- Employee-manager relationships
- Bill of materials (parent-child relationships)
- Finding duplicate records
SELECT e.employee_name, m.employee_name AS manager_name FROM employees e LEFT JOIN employees m ON e.manager_id = m.employee_id