Select max date from a group of columns of type date

Question

hi ,
my requirement is i have 5 columns
ID, date1,date2,date3,date4.
first column is integer type and is primary key and remaining all columns are type DATE
the values in the table are for example:
ID date1 date2 date3 date4
100 8/19/2007 4:29:44 PM 8/18/2007 3:50:34 PM 8/16/2007 3:20:55 PM 8/20/2007 5:19:24 PM
101 8/21/2007 5:29:44 PM 8/19/2007 4:20:34 PM 8/19/2007 4:29:44 PM 8/18/2007 2:50:45 PM
the output required is
ID closeddate
100 8/20/2007 5:19:24 PM
101 8/21/2007 5:29:44 PM
i want the max of all dates in all date columns in one single column for each row
the query which i tried is
select ID,max(closed_date)
from t1,TABLE(Date(date1,date2,date3,date4)) closeddate
but its not working
can any body help me out in solving this
thanks in advance

Answer 1

so use the NVL on each column. and set it to
something ridiculous, so it will always be less than
the other values. and then, if the ridiculous value
shows up, it means all the columns were null for that
row.Rather than relying on some rediculously small date use coalecse on each date column with the date column of intereste listed first. The order of the remaining terms in the coalesce statement is unimportant. e.g. on a table with three date columsn:
with x as (
  select 1 id, sysdate dte1, sysdate-1 dte2, sysdate+1 dte3 from dual union
  select 2, sysdate, null, null from dual union
  select 3, null, sysdate-1, null from dual union
  select 4, null, sysdate-1, sysdate+1 from dual union
  select 5, null, null, null from dual
select id,
       greatest( coalesce(dte1,dte2,dte3),
                 coalesce(dte2,dte3,dte1),
                 coalesce(dte3,dte1,dte2)) Max_Date
from x
ID                     MAX_DATE                 
1                      09-OCT-2007 12.15.44     
2                      08-OCT-2007 12.15.44     
3                      07-OCT-2007 12.15.44     
4                      09-OCT-2007 12.15.44     
5                      (null)
5 rows selecteThis way if they are all null, you get a null result, and don't need to handle your null value date as a special case. It also avoids the situation where the unlikely event occurs where your special null value date appears as actual data.