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
| Stu_Id | Stu_Name | Stu_Class |
| 1 | Komal | 10 |
| 2 | Ajay | 10 |
| 3 | Rakesh | 10 |
| 4 | Bhanu | 10 |
| 5 | Santosh | 10 |
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