1手动添加[主键约束]PK_Employees_EmpId
alter table Employees add constraint PK_Employees_EmpId primary key(EmpId)
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2手动为EmpName增加非空约束
alter table Employees alter column EmpName varchar(50) not null
3手动为EmpName增加唯一键约束
alter table Employees add constraint UQ_Employees_EmpName unique(EmpName)
go
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4删除唯一键约束
alter table Employees drop constraint UQ_Employees_EmpName
5为性别增加默认约束,使默认值为"男"
alter table Employees add constraint DF_Employees_EmpGender
default(1) for EmpGender
6为年龄增加检测约束 0-120含0和120
alter table Employees add constraint CK_Employees_EmpAge
check(EmpAge>=0 and EmpAge<=120)
7为性别增加检查约束 非 男 即 女
alter table Employees add constraint CK_Employees_EmpGender
check(EmpGender='男' or EmpGender='女')
8--为员工表增加外键约束
--首先，设置部门表中的DepId为主键,并且外键不能为空
alter table Department add constraint Pk_Deparment_DepId primary key(DepId)
alter table Employee alter column DepId int not null
alter table Employee add constraint FK_Employee_EmpDepId
foreign key(DepId) references Department(DepId) on delete cascade
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9一条语句删除多个约束
alter table Employees drop constraint FK_Employees_EmpDepId,
CK_Employees_EmpAge,
UQ_Employees_EmpName
10一条语句为表增加多个约束
alter table Employees add constraint
UQ_Employees_EmpName
unique(EmpName),
constraint
CKSSS
check(EmpAge>=0and EmpAge<=120)