Required SQL statement (8) integrity constraints of the database and SQL integrity

Required SQL statement (8) integrity constraints of the database and SQL integrity

Entity integrity
1. Define the primary key when creating a table

Create table Name
(
Sno int identity (1, 1 ),
Sname nvarchar (20 ),
-- Set the primary key
Primary key (Sno)
)
 
2. Add a primary key

Alter table name
Add constraint PK _ TABLE name_sno
Primary key (id)
Reference integrity 1. Define Foreign keys when creating a table

Create table Name
(
Sno int identity (1, 1) primary key,
Cno int not null,
Foreign key (cno) References
Table name 2 (Cno)
On Delete cascade -- cascade Delete
On update cascade -- cascade update
-- On delete on action delete Control
)
 
2. Add a foreign key
Alter table name
Add constraint FK _ TABLE name_table name 2
Foreign key (cid) references table name 2 (cid)
User-Defined integrity 1. Non-empty Constraints
Alter table name
Alter column name varchar (20) not null
 
2. unique constraints
Alter table name
Add constraint UQ _ TABLE name_column name unique (column)
 
3. Check Constraints
Alter table name
Add constraint CK _ TABLE name_column name check (age> 5)
 
4. Default Constraints
Alter table name
Add constraint DF _ TABLE name_column name default ('male ')
For gender
Delete constraint -- delete Constraint
Alter table Name drop constraint DF _ table name_column