Query to use GROUP BY multiple columns - sql

Question

I have a table full of patients/responsible parties/insurance carrier combinations (e.g. patient Jim Doe's responsible party is parent John Doe who has insurance carrier Aetna Insurance). For each of these combinations, they have a contract that has multiple payments. For this particular table, I need to write a query to find any parent/RP/carrier combo that has multiple contract dates in the same month. Is there anyway to do this?
Example table:
ContPat | ContResp | ContIns | ContDue
------------------------------------------------------
53 | 13 | 27 | 2012-01-01 00:00:00.000
53 | 13 | 27 | 2012-02-01 00:00:00.000
53 | 15 | 27 | 2012-03-01 00:00:00.000
12 | 15 | 3 | 2011-05-01 00:00:00.000
12 | 15 | 3 | 2011-05-01 00:00:00.000
12 | 15 | 3 | 2011-06-01 00:00:00.000
12 | 15 | 3 | 2011-07-01 00:00:00.000
12 | 15 | 3 | 2011-08-01 00:00:00.000
12 | 15 | 3 | 2011-09-01 00:00:00.000
In this example, I would like to generate a list of all the duplicate months for any Patient/RP/Carrier combinations. The 12/15/3 combination would be the only row returned here, but I'm working with thousands of combinations.
Not sure if this is possible using a GROUP BY or similar functions. Thanks in advance for any advice!

Answer 1

If all you care about is multiple entries in the same calendar month:
SELECT
ContPat,
ContResp,
ContIns,
MONTH(ContDue) as Mo,
YEAR(ContDue) as Yr,
COUNT(*) as 'Records'
FROM
MyTable
GROUP BY
ContPat,
ContResp,
ContIns,
MONTH(ContDue),
YEAR(ContDue)
HAVING
COUNT(*) > 1
This will show you any Patient/Responsible Party/Insurer/Calendar month combination with more than one record for that month.