Learning SQL--多表查询

Learning SQL --多表查询
1.笛卡尔积
SELECT e.fname,e.lname,d.name

FROM employee e JOIN department d;

2.内连接
SELECT e.fname,e.lname,d.name
FROM employee e JOIN department d
ON e.dept_id=d.dept_id;
==
SELECT e.fname,e.lname,d.name
FROM employee e INNER JOIN department d
ON e.dept_id=d.dept_id;
==
SELECT e.fname,e.lname,d.name
FROM employee e INNER JOIN department d
USING (dept_id);