select username,sid,serial# from v$session

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如下结果：

username          sid                serial#

----------------------------------------

NETBNEW          513              22974
NETBNEW          514              18183
NETBNEW          516              21573
NETBNEW          531              9
WUZHQ             532              4562

(2)找到要删除用户的sid,和serial，并删除

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如：你要删除用户'WUZHQ',可以这样做：

alter system kill session'532,4562'

(3)删除用户

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drop user username cascade

(**)如果在drop 后还提示ORA-01940:无法删除当前已链接的用户，说明还有连接的session，可以通过查看session的状态来确定该session是否被kill 了，用如下语句查看：

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select saddr,sid,serial#,paddr,username,status from v$session where username is not null

结果如下(以我的库为例)：

saddr                     sid           serial#            paddr              username              status

--------------------------------------------------------------------------------------------------------

564A1E28              513           22974            569638F4        NETBNEW             ACTIVE
564A30DC              514          18183            569688CC        NETBNEW            INACTIVE
564A5644              516           21573            56963340        NETBNEW            INACTIVE
564B6ED0              531           9                   56962D8C        NETBNEW            INACTIVE
564B8184              532          4562               56A1075C        WUZHQ                KILLED

status 为要删除用户的session状态，如果还为inactive，说明没有被kill掉，如果状态为killed，说明已kill。

由此可见，WUZHQ这个用户的session已经被杀死。此时可以安全删除用户。