Count records per month

Question

Hi,
there is two date columns "from" and "to" in the table "contracts" (contract validity, e.g. from 01.03.2012 to 31.12.2014). How to select the count of valid contratc per month ?
Result:
month valid contracts
03.2012 2341
04.2012 2355
Thanks in advance,
Michel

Answer 1

Hi, Michel,
Michel77 wrote:
Hi,
there is two date columns "from" and "to" in the table "contracts" (contract validity, e.g. from 01.03.2012 to 31.12.2014). How to select the count of valid contratc per month ?So, if the start_date is in March, 2012, and the end_date is in December, 2014, do you want that 1 contract to be counted 34 times, once for each month from March 2012 through December 2014?
Here's one way:
WITH     month_range     AS
     SELECT     TRUNC (MIN (start_date, 'MONTH'))     AS start_month
     ,     TRUNC (MAX (end_date,     'MONTH'))     AS end_month
     FROM     contracts
,     all_months     AS
     SELECT     ADD_MONTHS ( start_month
                  , LEVEL - 1
                  )          AS this_month
     ,     ADD_MONTHS ( start_month
                  , LEVEL
                  )          AS next_month
     FROM    month_range
     CONNECT BY     LEVEL <= 1 + MONTHS_BETWEEN ( end_month
                                             , start_month
SELECT       a.this_month
,       COUNT (c.start_date)     AS valid_contracts
FROM            all_months  a
LEFT OUTER JOIN contracts   c  ON  c.start_date          <  a.next_month
                              AND c.end_date          >= a.this_month
GROUP BY  a.this_month
ORDER BY  a.this_month
I hope this answers your question.
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Point out where the statment above is getting the wrong results, and explain, using specific examples, how you get the right results from the given data in those places.
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