文档解释
ORA-01940: cannot drop a user that is currently connected
Cause: Attempt was made to drop a user that is currently logged in.
Action: Make sure user is logged off, then repeat command.
ORA-01940: cannot drop a user that is currently connected这条错误信息指示，数据库正在尝试删除一个正在连接的用户。这是不允许的，因此ORACLE拒绝这么做。
官方解释
常见案例
案例1：某数据库用户在尝试删除另一个用户时收到以下错误消息：ORA-01940：“无法删除当前连接的用户”。
正常处理方法及步骤
SELECT * FROM V$SESSION WHERE USERNAME=’USER_TO_BE_DROPPED’;
2.若存在任何返回记录，立即终止这些会话：
ALTER SYSTEM KILL SESSION ‘sid,serial#’;
3.一旦所有会话与目标用户断开连接，即可尝试再次删除这些用户：
DROP USER USER_TO_BE_DROPPED;
