Answer Posted / satish reddy

Each table can have only one primary key; however, that key may consist of more than one column.

SQL> create table EMP(EMPNO Number(5),EMPNAME Varchar2(10),ADDRESS Varchar2(10),Constraint Multi_Constr
aint Primary Key(EMPNO,EMPNAME));

After creating table try to insert null value into EMPNAME Column, it will throw an error "cannot insert NULL into ("SCOTT"."EMP"."EMPNAME")"

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