How to unlock a locked table in a database

Data | database
When we operate the database, sometimes due to improper operation caused the database table is locked, so we often overwhelmed, do not know how to unlock these tables, in the Pl/sql Developer Tool menu "Tools" inside the "sessions" can be queried now existing sessions, But it's hard to find that the session is locked, so it's even harder to find the locked session, which is called a query to query the locked session. As follows:

select   Sn.username, M.sid,sn. serial#, m.type,         DECODE (m.lmode,                  0, ' None ',                  1, ' Null ',                  2, ' Row Share ',                  3, ' Row excl. ',                  4, ' Share ',                  5, ' s/row excl. ',                  6, ' Exclusive ',                  Lmode, LTRIM (To_char (Lmode, ' 990 '))                 ) lmode,         DECODE (m.request,                  0, ' None ',                  1, ' Null ',                  2, ' Row Share ',                  3, ' Row excl. ',                  4, ' Share ',                  5, ' s/row excl. ',                  6, ' Exclusive ',                  request, LTRIM (To_char (m.request, ' 990 '))                 ) request,          m.id1, m.id2    from V$session sn, v$lock m   WHERE (SN. SID = m.sid and m.request!= 0)         -there is a lock request that is blocked     & nbsp OR (    sn. SID = m.sid                         -There are no lock requests, but locked objects are locked by other session requests            and m.request = 0          and Lmode!= 4  & nbsp;       and (ID1, Id2) in (                         SELECT S.id1, s.id2                           from V$lock s                           WHERE Request!= 0 and s.id1 = m.id1                                 and S.id2 = M.id2)          order by ID1, Id2, m.request;

Through the above query know Sid and Serial# can kill the alter system kill session ' sid,serial# ';