1.查询用户的连接状态
Select username,sid,serial# from v$session where username='XY1027';

USERNAME                              SID    SERIAL#
------------------------------ ---------- ----------
XY1027                                 22          1
XY1027                                142          1

2.逐个删除
Alter system kill session'22,1';

3.删除用户
drop user xy1027 cascade;

4.检查状态

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：
-------------------------------------
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  &nbs