How to group these values month by month ?

Question

Hi,
I have a nice SQL statement which returns days by days, the values of a device.
WITH S1 AS
  (SELECT DATE1,
    ROUND(AVG(VALEUR),2) Debit
     FROM EVV_E032
    WHERE DATE1 BETWEEN TO_DATE('01012006000000', 'DDMMYYYYHH24MISS') AND TO_DATE('31122006235959', 'DDMMYYYYHH24MISS')
  AND CLEF_VAR =
    (SELECT CLEF_VAR FROM SITE_DEBIT_RIVIERE WHERE SITE = 'E032'
GROUP BY date1
SELECT NULL LINK    ,
  TO_CHAR(n, 'DD.MM'),
  NVL(ROUND(AVG(Debit),2), 0) "Débit"
   FROM
  (SELECT TRUNC(TRUNC(to_date(2006,'YYYY'),'year'), 'DD')-1 + level n,
    rownum jours
     FROM dual CONNECT BY level<=366
  ) days
LEFT JOIN s1
     ON days.n = TRUNC(date1,'DD')
GROUP BY n
ORDER BY nSample values :
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('10/02/2006 09:49:59','DD/MM/YYYY HH24:MI:SS') 1,63);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('21/02/2006 10:35:12','DD/MM/YYYY HH24:MI:SS') 1,68);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('21/02/2006 11:30:30','DD/MM/YYYY HH24:MI:SS') 0);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('23/02/2006 14:02:02','DD/MM/YYYY HH24:MI:SS') 0);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('23/02/2006 16:22:34','DD/MM/YYYY HH24:MI:SS') 0);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('30/04/2006 18:09:08','DD/MM/YYYY HH24:MI:SS') 1,72);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('20/05/2006 11:57:02','DD/MM/YYYY HH24:MI:SS') 1,72);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('07/06/2006 15:11:58','DD/MM/YYYY HH24:MI:SS') 1,79);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('08/06/2006 20:00:26','DD/MM/YYYY HH24:MI:SS') 1,82);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('19/06/2006 09:42:32','DD/MM/YYYY HH24:MI:SS') 1,72);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('20/06/2006 04:30:00','DD/MM/YYYY HH24:MI:SS') 1,82);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('20/06/2006 10:39:01','DD/MM/YYYY HH24:MI:SS') 1,72);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('24/06/2006 19:34:50','DD/MM/YYYY HH24:MI:SS') 1,82);
Insert into "EVV_E032" (DATE1,DEBIT) values (to_date('26/06/2006 14:37:26','DD/MM/YYYY HH24:MI:SS') 1,88);The output are values grouped day by day. I would like to group tehse values month by month, but could not figure how to do. Even though I am not a newbie newbie on SQL, this code is going far too much for me. I know some of you guys can handle this. I tried hard but coud not succeed. Could you help me ?
Regards, Christian.

Answer 1

Difficult to work out (read: too much hassle) with your data and sql, as you haven't provided a set of info for all the tables provided, but hopefully this will give you an idea:
with my_tab as (select trunc(sysdate)+30 dt, 1 val from dual union all
                select trunc(sysdate) dt, 2 val from dual union all
                select trunc(sysdate) dt, 20 val from dual union all
                select trunc(sysdate)+30 dt, 10 val from dual union all
                select trunc(sysdate)+60 dt, 6 val from dual)
-- end of mockup of table "my_tab"; see SQL below...
select trunc(dt, 'mm') dt, sum(val)
from   my_tab
group by trunc(dt, 'mm')
order by trunc(dt, 'mm');
DT          SUM(VAL)
01-MAR-09         22
01-APR-09         11
01-MAY-09          6