Mastering Oracle SQL学习笔记(join句法专题第四部份)
2.4.2
Equi-Joins
对
Non-Equi-Joins
在
Join
查询中如果使用等号操作符把两个表关联起来则为
Equi-Joins,
不是用等号操作符则为
Non-Equi-Joins
Equi-Joins:
SELECT s.name supplier_name, p.name part_name
FROM supplier s JOIN part p
ON s.supplier_id = p.supplier_id;
Non-Equi-Joins:
SELECT p.name part_name, c.inv_class inv_class
FROM part p JOIN inventory_class c
ON p.unit_cost BETWEEN c.low_cost AND c.high_cost;
2.4.3
Self Joins
就是一个表的行与该表的另外的行关联
1) SELECT e.lname employee, m.lname manager
FROM employee e JOIN employee m
ON e.manager_emp_id = m.emp_id;
Self outer joins:
SELECT e.lname employee, m.lname manager
FROM employee e LEFT OUTER JOIN employee m
ON e.manager_emp_id = m.emp_id;
Self non-equi-joins
1) SELECT d1.name team1, d2.name team2
FROM department d1 JOIN department d2
ON d1.dept_id != d2.dept_id;
2) SELECT d1.name team1, d2.name team2
FROM department d1 JOIN department d2
ON D1.DEPT_ID < D2.DEPT_ID;