Oracle常⽤查询语句⼀、查询锁表解锁语句
⾸先要⽤dba权限的⽤户登录，建议⽤，然后直接看sql吧
1. 如下语句查询锁定的表.
SELECT L.SESSION_ID SID,
S.SERIAL#,
L.LOCKED_MODE,
L.ORACLE_USERNAME,
L.OS_USER_NAME,
S.MACHINE,
S.TERMINAL,
O.OBJECT_NAME,
S.LOGON_TIME
FROM V$LOCKED_OBJECT L, ALL_OBJECTS O, V$SESSION S
WHERE L.OBJECT_ID = O.OBJECT_ID
AND L.SESSION_ID = S.SID
ORDER BY SID, S.SERIAL#;
2.然后删除掉系统锁定的此记录，其中SID和serial#为上⼀条sql查询出的第⼀个和第⼆个字段ALTER system KILL session 'SID,serial#';
⼆、查询当前数据库连接数，进程数，启动数据库
1、查询数据库当前进程的连接数：
  select count(*) from v$process;
2、查看数据库当前会话的连接数：
　select count(*) from v$session;
3、查看数据库的连接数：
select count(*) from v$session where status='ACTIVE';
4、查看当前数据库建⽴的会话情况：
select sid,serial#,username,program,machine,status from v$session;
5、查询数据库允许的最⼤连接数： 
select value from v$parameter where name = 'processes';
或者：show parameter processes;
6、查询所有数据库的连接数
selectschemaname,count(*)fromv$sessiongroupbyschemaname;
7、查询终端⽤户使⽤数据库的连接情况。
selectosuser,schemaname,count(*)fromv$sessiongroupbyschemaname,osuser;
8、查看当前不为空的连接
select * from v$session where username is not null
9、查看不同⽤户的连接数
select username,count(username) from v$session where username is not null group by username 10、查看连接数
select count(*) from v$session
11、并发连接数
Select count(*) from v$session where status='ACTIVE'　
12、最⼤连接
show parameter processes
12、修改连接
alter system set processes = value scope = spfile
13、修改数据库允许的最⼤连接数：
alter system set processes = 300 scope = spfile;
　(需要重启数据库才能实现连接数的修改)
14、重启数据库： 
  su - oracle
  sqlplus system/pwd as sysdba //进⼊sql
  startup //启动数据库
  lsnrctl start //启动监听
  sqlplus "/as sysdba"
  shutdown immediate;
  startup mount;
  alter database open;
15、查看当前有哪些⽤户正在使⽤数据： 
select osuser,a.username,cpu_time/executions/1000000||'s',sql_fulltext,machine
from v$session a,v$sqlarea b
where a.sql_address = b.address
order by cpu_time/executions desc;
备注：UNIX 1个⽤户session对应⼀个操作系统process，⽽Windows体现在线程。
16、oracle中查询被锁的表并释放session
SELECT A.OWNER,A.OBJECT_NAME,B.XIDUSN,B.XIDSLOT,B.XIDSQN,B.SESSION_ID,B.ORACLE_USERNAME, B.OS_USER_NAME,B.PROCESS, B.LOCKED FROM ALL_OBJECTS A,V$LOCKED_OBJECT B,SYS.GV_$SESSION C
WHERE ( A.OBJECT_ID = B.OBJECT_ID ) AND (B.PROCESS = C.PROCESS ) ORDER BY 1,2
17、查看占⽤系统io较⼤的session
SELECT se.sid,se.serial#,pr.SPID,se.username,se.inal,se.program,se.MODULE,se.sql_address,st.event,st.p1text,si.physical_reads,si.block_ch FROM v$session se,　v$session_wait st,v$sess_io si,v$process pr
WHERE st.sid=se.sid　AND st.sid=si.sid AND se.PADDR=pr.ADDR AND se.sid>6　AND st.wait_time=0 AND st.event NOT LIKE '%SQL%' ORDER BY physica
18、出耗cpu较多的session
select a.sid,spid,status,substr(a.program,1,40) inal,osuser,value/60/100 value
from v$session a,v$process b,v$sesstat c
where c.statistic#=12 and c.sid=a.sid and a.paddr=b.addr order by value desc
查询session被锁的sql可以⽤⼀下语句
select sys.v_$session.osuser,sys.v_$session.machine,v$lock.sid,
  sys.v_$session.serial#,
  decode(pe,　'MR', 'Media Recovery',　'RT','Redo Thread',　'UN','User Name',  'TX', 'Transaction','TM','DML','UL', 'PL/SQL User Lock',　'DX', 'Distributed
Xaction','CF', 'Control File',　'IS', 'Instance State',　'FS', 'File Set',　'IR',
'Instance Recovery',　'ST', 'Disk Space Transaction',　'TS', 'Temp Segment',  'IV',
'Library Cache Invalida-tion',　'LS', 'Log Start or Switch',　'RW', 'Row Wait',常用的sql查询语句有哪些
  'SQ', 'Sequence Number','TE', 'Extend Table',　'TT', 'Temp Table',　'Unknown')            LockType,
  rtrim(object_type) || ' ' || rtrim(owner) || '.' || object_name object_name,
  decode(lmode, 0, 'None',
  1, 'Null',
  2, 'Row-S',
  3, 'Row-X',
  4, 'Share',
  5, 'S/Row-X',
  6, 'Exclusive', 'Unknown') LockMode,
  decode(request, 0, 'None',
  1, 'Null',
  2, 'Row-S',
  3, 'Row-X',
  4, 'Share',
  5, 'S/Row-X',
  6, 'Exclusive', 'Unknown') RequestMode,
  ctime, block b
  from v$lock, all_objects, sys.v_$session
  where v$Lock.sid > 6
  and sys.v_$session.sid = v$lock.sid
  and v$lock.id1 = all_objects.object_id;

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