一 、 多表操作
select * from person,dept
二 、多表联合操作
select * from person,dept where person.dept_id =dept.did
select * from person,dept where person.dept_id =dept.did and person.salary >3000
三、多表连接查询
左连接查询 （以左表作为基准）
select *from person left JOIN dept on person.dept_id = dept.did
内连接查询
select * from person inner JOIN dept where person.dept_id =dept.did
4.全连接查询 full JOIN
select * from person LEFT JOIN dept ON person.dept_id = dept.did
UNION ALL
select * from person RIGHT JOIN dept on person.dept_id = dept.did;
二 、 复杂的多表查询 。
1. 查询出 教学部 年龄大于20岁,并且工资小于40000的员工,按工资倒序排列.(要求:分别使用多表联合查询和内连接查询)
select * from person inner join dept on person.dept_id = dept.did and dept.dname = ‘教学部‘ and person.age >20 and salary <40000 order by person.salary asc
