SqlServer--代码创建约束

--通过t-sql语句来创建约束

------------------------------------------------------------

--新建一张表：员工信息表

create table Employees

(

EmpId int identity(1,1),

EmpName varchar(50),

EmpGender char(2),

EmpAge int,

EmpEmail varchar(100),

EmpAddress varchar(500)

)

create table Department

(

DepId int identity(1,1) ,

DepName varchar(50)

)

--=====手动增加约束==========

--手动删除一列(删除EmpAddress列)

alter table Employees drop column EmpAddress

--手动增加一列(增加一列EmpAddr varchar(1000))

alter table Employees add EmpAddr nvarchar(1000)

--手动修改一下EmpEmail的数据类型(varchar(200))

alter table Employees alter column EmpEmail varchar(200)

--为EmpId增加一个主键约束

alter table Employees add constraint PK_Employees_EmpId primary key(EmpId)

--非空约束,为EmpName增加一个非空约束 not null(修改列)

alter table Employees alter column EmpName varchar(50) not null

--为EmpName增加一个唯一约束

alter table Employees add constraint UQ_Employees_EmpName unique(EmpName)

--为性别增加一个默认约束，默认为‘男‘

alter table Employees add constraint DF_Employees_EmpGender default(‘男‘) for EmpGender

--为性别增加一个检查约束，要求性别只能是：‘男‘ or ‘女‘

alter table Employees add constraint CK_Employees_EmpGender check(EmpGender=‘男‘ or EmpGender=‘女‘)

--为年龄增加一个检查约束：年龄必须在-120岁之间，含岁与岁。

alter table Employees add constraint CK_Employees_EmpAge check(EmpAge>=0 and EmpAge<=120)

--创建一个部门表，然后为Employee表增加一个DepId列。

alter table Employees add EmpDepId int not null

--为Department表设置主键。主键列是：DepId

alter table Department add constraint PK_Department_DepId primary key(DepId)

--增加外键约束

alter table Employees add constraint FK_Employees_Department foreign key(EmpDepId) references Department(DepId) -- on delete cascade

--删除约束

alter table Employees drop constraint

FK_Employees_Department,

CK_Employees_EmpAge,

CK_Employees_EmpGender,

DF_Employees_EmpGender,

UQ_Employees_EmpName

--通过一条代码来增加多个约束

alter table Employees add

constraint FK_Employees_Department foreign key(EmpDepId) references Department(DepId),

constraint CK_Employees_EmpAge check(EmpAge>=0 and EmpAge<=120),

constraint CK_Employees_EmpGender check(EmpGender=‘男‘ or EmpGender=‘女‘)

---创建表的同时就为表增加约束

create table Employees

(

EmpId int identity(1,1) primary key,

EmpName varchar(50) not null unique check(len(EmpName)>2),

EmpGender char(2) default(‘男‘),

EmpAge int check(EmpAge>0 and EmpAge<120),

EmpEmail varchar(100) unique,

EmpAddress varchar(500) not null,

EmpDepId int foreign key references Department(DepId) on delete cascade

)

create table Department

(

DepId int identity(1,1) primary key,

DepName varchar(50) not null unique

)