视图操作：
1.左连接查询
select * from person left join dept on person.dept_id = dept.did
2. 右连接
3. 内连接 inner join
4. UNION ALL 全连接
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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
2.查询每个部门中最高工资和最低工资是多少,显示部门名称
select dept.dname , MAX(salary),MIN(salary) from person LEFT JOIN dept on person.dept_id =dept.did group by person.dept_id
2.求最大工资那个人的姓名和薪水
1.求最大工资
select max(salary) from person;
2.求最大工资那个人叫什么
select name,salary from person where salary=53000;
合并
select name,salary from person where salary=(select max(salary) from person);
3. 求工资高于所有人员平均工资的人
1.求平均工资
select avg(salary) from person;
2.工资大于平均工资的 人的姓名、工资
select name,salary from person where salary > 21298.625;
合并
select name,salary from person where salary >(select avg(salary) from person);
