To_char function not working

Question

hi,
I want to get the max dates on format MM/DD/YYYY. the problem is it only works on
select distinct
t.id,
max(to_char (t.tr_date,'MM/DD/YYYY')) as transaction_date,
s.contract_date,
max(i.start_date) as start_date,
max(i.end_date) as end_date
from trans_history t,
subscription s,
inv i
where t.prod='FTU'
and t.tr_date >='01-January-2010'
and s.id=t.id
and i.id=t.id
and t.id=1983634
group by
t.id,
s.contract
result:
Id Transaction Date Contract Start Date End Date
1983634 03/10/2010 11/01/2008 17/03/2010 29/03/2010
then if I change the query like below: im not getting the max values of start date and end date
select distinct
t.id,
max(to_char (t.tr_date,'MM/DD/YYYY')) as transaction_date,
s.contract_date,
max(to_char(i.start_date,'MM/DD/YYYY')) as start_date,
max(to_char(i.end_date,'MM/DD/YYYY')) as end_date
from trans_history t,
subscription s,
inv i
where t.prod='FTU'
and t.tr_date >='01-January-2010'
and s.id=t.id
and i.id=t.id
and t.id=1983634
group by
t.id,
s.contract
I'm wondering why to_char only works on t.tr_date field.
please help.

Answer 1

Hi,
Almost always, TO_CHAR is the last operation you do to DATEs. Do things like MAX before you convert the DATE to a string:
to_char ( max (t.tr_date)
        , 'MM/DD/YYYY'
        )When comparing the followig strings
'12/01/2008'
'07/01/2009'
'01/30/2010'the greatest is '12/01/2008', because '12' is greater than '07' and '01'.
You can change the default format for all DATEs in your session like this:
ALTER SESSION  SET  NLS_DATE_FORMAT = 'MM/DD/YYYY';Then you might not need TO_CHAR at all.
Edited by: Frank Kulash on Jul 23, 2010 6:51 AM