SQL PRIMARY KEY Constraint

The PRIMARY KEY constraint is used to uniquely identifies each record in a database table. The Primary keys in a table contains a unique values. It should contain NULL values. The Table contain a primary key and each table have only primary key.

Understand with Example

The Tutorial illustrate an example to understand SQL PRIMARY KEY Constraint. In this example, we create a table 'Stu_Class_10.The create  statement is used to create a table 'Stu_Class_10'.The following SQL creates a PRIMARY KEY on the "Stu_Id" when the" Stu_Class_10" table is created.

Create Table Stu_Class_10

create table Stu_Class_10(
Stu_Id integer(2) NOT NULL,
Stu_Name varchar(15),
Stu_Class  varchar(10),
PRIMARY KEY(Stu_Id))

Insert data into Stu_Class_10

The insert into statement is used to add the records or rows to the table 'Stu_Class_10'. 

insert into Stu_Class_10 values(1,'Komal',10)
insert into Stu_Class_10 values(2,'Ajay',10)
insert into Stu_Class_10 values(3,'Rakesh',10)
insert into Stu_Class_10 values(4,'Bhanu',10)
insert into Stu_Class_10 values(5,'Santosh',10)

Stu_Class_10