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Primary Key Constraint In SQL

 Primary Key::constraint ======================  ->It is combination of Unique and not null ->Restricted Duplicates and Nulls ->A table is having Only one primary Key At column Level:: ================= EX:: SQL> create table test2(eid int primary key,ename varchar2(10) primary key); create table test2(eid int primary key,ename varchar2(10) primary key)                                                           * ERROR at line 1: ORA-02260: table can have only one primary key SQL> create table test2(eid int primary key,ename varchar2(10)); Table created. SQL> insert into test2 values(1,'sam'); 1 row created. SQL> insert into test2 values(2,'dan'); 1 row created. SQL> select * from test2;        EID ENAME ---------- ----------          1 sam        ...