常用SQL语句


创建数据库

create database MyDb

on

(name='MyDb_Data',FileName='E:\Temp\MyDb.mdf')

log on

(name='MyDb_Log',FileName='E:\Temp\MyDb.mdf')
删除数据库

drop database MyDb

创建表

use MyDb //通过use命令先连接到数据库

create table Department

(

DepartmentId int primary key,

DepartmentName nvarchar(20) not null //not null指示不能为空

)

create table Employee

(

EmployeeId nchar(10) primary key,

EmployeeName nvarchar(20) not null,

DateOfBirth datetime,

DepartmentId int,

Salary float,

Sex nchar(1)

)

添加数据

insert into Department (DepartmentId,Departmentname)

values (1,'开发科')

insert into Department (DepartmentId,Departmentname)

values (2,'销售科')

insert into Department (DepartmentId,Departmentname)

values (3,'财务科')

insert into Employee(EmployeeId,Employeename,DateOfBirth,DepartmentId,

Salary,Sex)

values('E001','火狐','1989-10-6',1,9000,'男')

insert into Employee(EmployeeId,Employeename,DateOfBirth,DepartmentId,

Salary,Sex)

values('E002','路人','1985-10-6',2,6000,'女')

更新数据

update Employee

set Salary=Salary+500,EmployeeName='张四' //可以修改多个

where EmployeeId='E003'

删除数据

delete from Department //如果不写条件则全部删除

where DepartmentId=10

查询数据

select * from Employee //查询Employee表中的所有信息

where Salary>=6000 //查询Employee表中Salary>=6000 的信息

select top 2 * from Employee //查询Employee表中的所有信息的前两条

聚合函数

***G 返回一组数据的平均值，NULL将被忽略

COUNT 返回一组数据的项数，始终返回int型值

MAX 返回一组数据中的最大值，NULL将被忽略

MIN 返回一组数据中的最小值，NULL将被忽略

SUM 返回一组数据中的数据的和，NULL将被忽略

select avg(Salary) from Employee //查询所有的平均工资

select avg(Salary) from Employee whereDepartmentId=1 //只查询开发科的平均工资

select count(*) from Employee where sex='男' //查询男性的数量

select max(salary) as 最高工资, min(salary) as 最低工资

from Employee

select sum(salary) from Employee

未完待续！