Manually set data constraints for Databases

Manually set data constraint 1 manually add [primary key constraint] constraint (EmpId) www.2cto. com2 manually add non-null constraint for EmpName altertableEmployeesaltercolumnEmpNamevarchar (50) notnull

Manually set data constraint 1 manually add [primary key constraint] PK_Employees_EmpId alter table Employees add constraint PK_Employees_EmpId primary key (EmpId) manually add non-empty constraint alter table Employees alter column EmpName varchar (50) not null for EmpName on www.2cto.com 2

Manually set data constraints for Databases

1 manually add the [primary key constraint] PK_Employees_EmpId

Alter table Employees add constraint PK_Employees_EmpId primary key (EmpId)

Www.2cto.com

2 manually add non-empty constraints for EmpName

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

3 manually add a unique key constraint for EmpName

Alter table Employees add constraint UQ_Employees_EmpName unique (EmpName)

Go

Www.2cto.com

4. Delete the unique key constraint.

Alter table Employees drop constraint UQ_Employees_EmpName

5. Add a default constraint for gender so that the default value is "male"

Alter table Employees add constraint DF_Employees_EmpGender

Default (1) for EmpGender

6 Add detection constraints for age 0-1 20 containing 0 and 120

Alter table Employees add constraint CK_Employees_EmpAge

Check (EmpAge> = 0 and EmpAge <= 120)

7. Add check constraints for Gender: Non-male or female

Alter table Employees add constraint CK_Employees_EmpGender

Check (EmpGender = 'male' or EmpGender = 'femal ')

8 -- add a foreign key constraint to the employee table

-- First, set the DepId in the department table as the primary key, and the foreign key cannot be blank.

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

Www.2cto.com

9 Delete multiple constraints in one statement

Alter table Employees drop constraint FK_Employees_EmpDepId,

CK_Employees_EmpAge,

UQ_Employees_EmpName

One statement adds multiple constraints to the table.

Alter table Employees add constraint

UQ_Employees_EmpName

Unique (EmpName ),

Constraint

CKSSS

Check (EmpAge> = 0and EmpAge <= 120)