Unique

UNIQUE(Integrity Constraint)
            The purpose of a unique key is to ensure that information in the columns is unique i.e. a value entered in column defined in the unique constraint must not be repeated across the column. A table may have many unique keys.
Syntax:- 1.Columnname datatype(size) Unique     à  Column level
               2. Unique (columname,colname,----)       à  Table level
Ex:- 1  create table vision2(eno number(5) unique,na varchar2(20),sal number(5));
        2  Create table vision3(eno number(5),code number(5),sal number(5),
unique (eno,code));

       3  insert into vision2 values(100,’prasad’,3200);
4 insert into vision2 values(100,’vani’,4300);
5 insert into vision3 values(100,10,1000);
6 insert into vision3 values(200,10,2000);
7 insert into vision3 values(200,10,3200);

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