Search notes:

ORA-01940: cannot drop a user that is currently connected

A user that has open sessions cannot be dropped, in such a case, the following statement would throw the error meesage ORA-01940: cannot drop a user that is currently connected:

drop user k cascade;

Generate alter system kill session statements for each session that the user has open:

select
  'alter system kill session ''' || sid || ',' || serial# || ''' immediate;'  stmt
from
   gv$session
where
   username ='K';

The following anonymous PL/SQL block uses execute immediate to execute the statements created with the previous select statement.

In addition, it uses the force option available with 23c to immediatly terminate all sessions of a given user:

begin
   for r in (
      select
        'alter system kill session ''' || sid || ',' || serial# ||
           case when dbms_db_version.version >= 23 then ' force' end ||
        ''''   stmt
      from
         gv$session
      where
         username ='GTFS_ZURICH') loop

         execute immediate r.stmt;
    end loop;
end;
/

ORA-01940: cannot drop a user that is currently connected

See also