Greatest Function...

Question

Hi,
I havea query like this:
select trunc(GREATEST(MAX(TRAVEL_START),
                        MAX(TRAVEL_STOP),
                        MAX(LABOR_START),
                        MAX(LABOR_STOP)))
from t1the columns are combinaton such that user can enter travel_start and travel_stop combination OR labor_start and labor_stop combination or both or none of them...
Now,
the query fails when user inputs any one of the combination.. so for eg. user enters labor_start and labor_stop but does not enter Travel start and stop combinaton(i.e. null is stored in travel start/stop) the greatest returns null instead of returning greatest from labor_start/stop combinaton.
What should be done to rectify this..
thx

Answer 1

I missed the requirement that the output should be null when all 4 columns are null, so I added a NULLIF function to achieve the desired result. The example now becomes:
SQL> var TRAVEL_START varchar2(8)
SQL> var TRAVEL_STOP varchar2(8)
SQL> var LABOR_START varchar2(8)
SQL> var LABOR_STOP varchar2(8)
SQL> exec :TRAVEL_START := null;
PL/SQL-procedure is geslaagd.
SQL> exec :TRAVEL_STOP := null;
PL/SQL-procedure is geslaagd.
SQL> exec :LABOR_START := '01012006';
PL/SQL-procedure is geslaagd.
SQL> exec :LABOR_STOP := '31122006';
PL/SQL-procedure is geslaagd.
SQL> select trunc
  2         ( greatest
  3           ( max(to_date(:TRAVEL_START,'ddmmyyyy'))
  4           , max(to_date(:TRAVEL_STOP,'ddmmyyyy'))
  5           , max(to_date(:LABOR_START,'ddmmyyyy'))
  6           , max(to_date(:LABOR_STOP,'ddmmyyyy'))
  7           )
  8         )
  9    from dual
10  /
TRUNC(GREATEST(MAX(
1 rij is geselecteerd.
SQL> select nullif
  2         ( trunc
  3           ( greatest
  4             ( nvl(max(to_date(:TRAVEL_START,'ddmmyyyy')),to_date('1','j'))
  5             , nvl(max(to_date(:TRAVEL_STOP,'ddmmyyyy')),to_date('1','j'))
  6             , nvl(max(to_date(:LABOR_START,'ddmmyyyy')),to_date('1','j'))
  7             , nvl(max(to_date(:LABOR_STOP,'ddmmyyyy')),to_date('1','j'))
  8             )
  9           )
10         , to_date('1','j')
11         )
12    from dual
13  /
NULLIF(TRUNC(GREATE
31-12-2006 00:00:00
1 rij is geselecteerd.
SQL> exec :LABOR_START := null;
PL/SQL-procedure is geslaagd.
SQL> exec :LABOR_STOP := null;
PL/SQL-procedure is geslaagd.
SQL> select nullif
  2         ( trunc
  3           ( greatest
  4             ( nvl(max(to_date(:TRAVEL_START,'ddmmyyyy')),to_date('1','j'))
  5             , nvl(max(to_date(:TRAVEL_STOP,'ddmmyyyy')),to_date('1','j'))
  6             , nvl(max(to_date(:LABOR_START,'ddmmyyyy')),to_date('1','j'))
  7             , nvl(max(to_date(:LABOR_STOP,'ddmmyyyy')),to_date('1','j'))
  8             )
  9           )
10         , to_date('1','j')
11         )
12    from dual
13  /
NULLIF(TRUNC(GREATE
1 rij is geselecteerd.Regards,
Rob.