Constraint in SQL

Constraint: 

1. Primary Key
2. Not Null
3. Check and
4. References.

Creating Table using primary key and not null

create table student

        (

        rollno number primary key,

        name varchar2(15) not null,

        Branch varchar2(5),

        gender varchar2(7),

        DOB date,

        email_id varchar2(25),

        Address varchar2(25),

      phone_no number

     );

Creating Table using check and References

create table student_marks

   (

    rollno number references students_035,

    marks number

    constraint check_marks check(marks between 0 and 100)

    );

We apply the check Constraint on marks so if marks is not between the 0 and 100 then sql command is violated.

Example:

SQL> insert into student_marks values(1,67);

1 row created.

SQL> insert into student_marks values(40,107);

insert into student_marks values(40,107)

*

ERROR at line 1:

ORA-02290: check constraint (SCOTT.CHECK_MARKS) violated

Note: All commands are apply on above two tables for better understanding male your own table and attributes.
Query and any doubts please leave in comments.

Author : Unknown

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