Add another Primary key column problem

Question

Hi all
I do not Add primary key in existing table .how it possiable
say I have Existing Table
EMPNO NUMBER(4), primary key
ENAME VARCHAR2(10 BYTE),
JOB VARCHAR2(9 BYTE),
EMPSLNO VARCHAR2(10 BYTE)
Now Add another Primary key column(EMPSLNO)
my coding this
ALTER TABLE EMP_TEST ADD (
CONSTRAINT PK_EMP_TEST PRIMARY KEY (EMPSLNO))
but error message
Error on line 0
ALTER TABLE EMP_TEST ADD (
CONSTRAINT PK_EMP_TEST PRIMARY KEY (EMPSLNO))
ORA-02260: table can have only one primary key

Answer 1

..Or, too much few information, wild guess, (composite index)
Do this :
ALTER TABLE <your_table> ADD (
     CONSTRAINT PK_mycode PRIMARY KEY (head_code,item_code )
          USING INDEX TABLESPACE tbls_index;