有关数据库的一些基本知识

新建数据库表

create table employee(    eid int(15) primary key auto_increment,    ename varchar(20) not null,    salary float(9,2) not null,    deptid int(15) not null    );

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1、用两种方式根据部门号从高到低，工资从低到高列出每个员工的信息

select * from employee order by deptid desc,salary;

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2、列出各个部门中工资高于本部门的平均工资的员工数和部门号，并按部门号排序

• 首先，下面这条语句是查询各个部门的平均工资

select avg(salary) from employee group by deptid;

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order by 与 group by 的区别：

• order by 是排序；group by 是分组。 具体区别，再写个例子，一看便知：

select * from employee group by deptid desc,salary;

select * from employee group by deptid desc;

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