SQL - Group By / Order by question

Question

I have a table MESSAGE with two columns.
SQL> desc message
Name Null? Type
MESSAGE_TEXT VARCHAR2(50)
MESSAGE_DATE DATE
My requirements are:
1) Display MESSAGE_TEXT and MESSAGE_DATE (Date only, no time component) in MESSAGE_DATE order (including time component).
2) Do not show multiple rows which have the same MESSAGE_TEXT and trunc(MESSAGE_DATE).
Given the following data:
SQL> select * from message;
MESSAGE_TEXT MESSAGE_DATE
Message Group 1 10/15/2002 13:00:00
Message Group 1 10/15/2002 14:00:00
Message Group 1 10/16/2002 15:00:00
Message Group 2 10/15/2002 14:00:00
Message Group 2 10/15/2002 16:00:00
Message Group 3 10/15/2002 13:30:00
Message Group 3 10/15/2002 17:00:00
I should return:
MESSAGE_TEXT MESSAGE_DATE
Message Group 1 10/15/2002
Message Group 3 10/15/2002
Message Group 2 10/15/2002
Message Group 1 10/16/2002
My first attempt to do this was:
SELECT MESSAGE_TEXT
, TO_CHAR(MESSAGE_DATE,'MM/DD/YYYY') FDATE
FROM MESSAGE
GROUP BY MESSAGE_TEXT, TO_CHAR(MESSAGE_DATE,'MM/DD/YYYY')
ORDER BY FDATE
but this did not work because it returned:
MESSAGE_TEXT FDATE
Message Group 1 10/15/2002
Message Group 2 10/15/2002
Message Group 3 10/15/2002
Message Group 1 10/16/2002
which violates requirement 1). Message Group 3 should appear before Message Group 2 because 13:30 comes before 14:00.
I ended up doing the following:
SELECT MESSAGE_TEXT
, TO_CHAR(MESSAGE_DATE,'MM/DD/YYYY') FDATE
FROM MESSAGE M1
WHERE NOT EXISTS
(SELECT *
FROM MESSAGE M2
WHERE M2.MESSAGE_TEXT = M1.MESSAGE_TEXT
AND TRUNC(M2.MESSAGE_DATE) = TRUNC(M1.MESSAGE_DATE)
AND M2.MESSAGE_DATE < M1.MESSAGE_DATE)
ORDER BY M1.MESSAGE_DATE
This gives me the right results, but surely there is a better way or ways. Please help.

Answer 1

SELECT   message_text,
         message_date_only AS message_date
FROM     (SELECT   message_text,
                   TO_CHAR (message_date, 'MM/DD/YYYY') AS message_date_only,
                   MIN (message_date) AS min_message_date_and_time
          FROM     message
          GROUP BY message_text, TO_CHAR (message_date, 'MM/DD/YYYY'))
ORDER BY min_message_date_and_time;
MESSAGE_TEXT    MESSAGE_DATE
Message Group 1 10/15/2002
Message Group 3 10/15/2002
Message Group 2 10/15/2002
Message Group 1 10/16/2002
4 rows selected.