10일 20일 30일 1 1 2 SLEEP20 2 3 dbms_pipe.receive_me 1 4 OR 1 5 PG_SLEEP20 2 6 WAITFOR 7 dbms_pipe.receive_messagea20 1 1 2 dbms_pipe.receive_me 3 PG_SLEEP20 4 SLEEP20 5 OR 6 WAITFOR 7 dbms_pipe.receive_messagea20 1 1 2 dbms_pipe.receive_me 1 3 PG_SLEEP20 1 4 SLEEP20 5 OR 6 WAITFOR 7 dbms_pipe.receive_messagea20 11위 - 20위