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UNIQUE KEY Constraints

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create table student(Roll_no number(10) Unique, Student_name varchar(20), Dept_name varchar(5));

insert into student(Roll_no, Student_name, Dept_name) values(10001,'jhon','cse')
insert into student(Roll_no, Student_name, Dept_name) values(10002,'hari','it')
insert into student(Roll_no, Student_name, Dept_name) values(10001,'raju','ME')
insert into student(Roll_no, Student_name, Dept_name) values(null,'raju','ME')

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