Need help with select that month range with flexible first date

Question

Hello everyone,
I am trying to create a selection of month range (will be in a WITH clause) for a report to display monthly data. But the first month start date can be any date. (Not necessarily the first date of the month)
Examples:
Report input parameters:
Start Date: 08/10/12
End Month: Dec 2012
I was trying to build a with select that will list
Month_Start, Month_End
08/10/12, 31/10/12
01/11/12, 30/11/12
01/12/12, 31/12/12
OR
Month_Start, Next_Month
08/10/12, 01/11/12
01/11/12, 01/12/12
01/12/12, 01/01/13
End month is optional, so if no value the select will list only
08/10/12, 01/11/12
Oracle Database Details is
Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - 64bit Production
PL/SQL Release 11.1.0.7.0 - Production
My code so far is
VARIABLE  P50_START_DATE  VARCHAR2 (10)
VARIABLE  P50_END_MONTH    VARCHAR2 (10)
EXEC  :P50_START_DATE  := '10/10/2012';
EXEC  :P50_END_MONTH   := '31/12/2012';
  SELECT  to_char(:P50_START_DATE) AS start_date
        ,  ADD_MONTHS( TRUNC(to_date(:P50_START_DATE,'DD/MM/YYYY'),'MONTH'), 1) AS next_month
  FROM dual
  union
   SELECT to_char(ADD_MONTHS( TRUNC(to_date(:P50_START_DATE,'DD/MM/YYYY'),'MONTH'), ROWNUM-1)) AS start_date
   ,      ADD_MONTHS( TRUNC(to_date(:P50_START_DATE,'DD/MM/YYYY'),'MONTH'), ROWNUM) AS next_month
   --, rownum
   from all_objects
   where
   rownum <= months_between(to_date(NVL(:P50_END_MONTH, :P50_START_DATE),'DD/MM/YYYY'), add_months(to_date(:P50_START_DATE,'DD/MM/YYYY'), -1))
   and rownum > 1If I put comment – on line and rownum > 1, as
-- and rownum > 1The result I get is
START_DATE                     NEXT_MONTH               
01/10/12                       01/10/12                 
01/11/12                       01/11/12                 
01/12/12                       01/01/13                 
10/10/2012                     01/11/12    But when I try to remove the duplicate period (of the first month) out by restrict rownum, it do not return any rows for the second select at all. The result I get is:
START_DATE                     NEXT_MONTH               
10/10/2012                     01/11/12    Can anyone advise what wrong with the select statement ?
Thanks a lot in advance,
Ann

Answer 1

Hi,
Here's one way:
WITH   params      AS
     SELECT     TO_DATE (:p50_start_date, 'DD/MM/YYYY')     AS start_date
     ,     TO_DATE (:p50_end_month,  'DD/MM/YYYY')     AS end_date
     FROM     dual
SELECT     GREATEST ( start_date
           , ADD_MONTHS ( TRUNC (start_date, 'MONTH')
                        , LEVEL - 1
          )               AS month_start
,     LEAST     ( end_date
          , ADD_MONTHS ( TRUNC (start_date, 'MONTH')
                      , LEVEL
                    ) - 1
          )               AS month_end
FROM    params
CONNECT BY     LEVEL     <= 1 + MONTHS_BETWEEN ( end_date
                                  , TRUNC (start_date, 'MONTH')
;:p50_end_month doesn't have to be the last day of the month; any day will work.
If you want to generate a Counter Table containing the integers 1 througn x in SQL, you could say
SELECT  ROWNUM  AS n
FROM    all_objects
WHERE   ROWNUM  <= x
;but, starting in Oracle 9.1, it's much faster to say
SELECT  LEVEL   AS n
FROM    dual    -- or any table containing exactly 1 row
CONNECT BY  LEVEL <= x
;Also, x can be greater than the number of rows in all_objects.