How to Know the PID of a user in Oracle

COL     DATETIME     FORMAT A20
COL    USR         FORMAT A10

SELECT     A.USERNAME USR,
    A.STATUS,A.SID,
    A.SERIAL#,
    LTRIM(RTRIM(TO_CHAR(A.LOGON_TIME,'DD/MM/YYYY HH:MM:SS'))) DATETIME,
    B.SPID
FROM     V$SESSION A,V$PROCESS B
WHERE     A.USERNAME IS NOT NULL
AND     A.PADDR=B.ADDR
AND     (B.SPID=UPPER('&&PIDUSR')
or     a.username=upper('&&PIDUSR'))
/
UNDEFINE PIDUSR