The user cannot be removed from Oracle, prompting "Unable to delete the currently connected user"

Scenario 1: Close the database and restart.

Scenario 2:

Alter user XXX account lock;
SELECT * from v$session WHERE username= ' lgdb ';
Alter system kill session ' xx,xx ' drop user xx cascade;

(1) View the user's connection status

Select username,sid,serial# from V$session;

(2) Find the SID to delete the user, and serial, and remove

Alter system kill session ' xx,xx ' drop user xx cascade;

The user cannot be removed from Oracle, prompting "Unable to delete the currently connected user"