SQL query using MAX function

Question

I am trying to only display the records where the 'date_entered' is the most recent date per case number.
SELECT distinct c.case_number, u.email,c.assigneddate_chart,
--m.date_entered,
max(m.date_entered)as last_date_entered,
trunc(sysdate)-trunc(c.assigneddate_chart)days_late,
trunc(sysdate)-trunc(m.date_entered)addl_days_late
from chart c, chart_user_roles u,comments m
where
(c.case_status IN ('Open','Pending')) and
c.case_number=m.case_number
group by c.case_number,
u.email,c.assigneddate_chart,m.date_enteredRight now, this is the output im am getting.
Output:
CASE_NUMBER------EMAIL---------ASSIGNEDDATE_CHART---LAST_DATE_ENTERED---DAYS_LATE--ADDL_DAYS_LATE
[email protected]----06-NOV-09-----------------31--------------------11
[email protected]----10-NOV-09-----------------31---------------------7
[email protected]----06-NOV-09-----------------31--------------------11
[email protected]----06-NOV-09-----------------31--------------------11
[email protected]----06-NOV-09-----------------31--------------------11
[email protected]----03-NOV-09-----------------34--------------------14
I am wanting to achieve this output:
Therefore, based on the data below, the only records that i am wanting to display are:
[email protected]----10-NOV-09-----------------31---------------------7
[email protected]----03-NOV-09-----------------34--------------------14
Thanks
Deanna

Answer 1

Is there a reason that you have a DISTINCT in your query? It always makes me nervous to see that where it's not clearly necessary because it frequently means that a developer is missing a join condition and is using the DISTINCT to mask that fact.
On to the meat of your question, though, is there a potential for ties? If so, how do you want to handle that-- do you want two rows for that case, do you want to break the tie using some other column, do you want to pick an arbitrary row? If you want to pick an arbitrary row
SELECT case_number, email, assignedDate_chart, last_date_entered, days_late, addl_days_late
  FROM (
    SELECT a.*, row_number() over (partition by case_number order by date_entered) rn
      FROM (<<your query>>) a
WHERE rn = 1If you want to do something else, just adjust the analytic function and use RANK or add a tie-breaker to the ORDER BY.
Justin