SQL Server query without using loops

Question

I have a Payment table that looks a little like this:

Id (int identity)
CustomerId (int)
PaymentDate (SmallDateTime)

Now I want to write a query that will find those customers that have made three payments within a period of three months. Given the following data:

Id   CustomerId   PaymentDate (YYYY-MM-DD)
------------------------------------------
1    1            2010-01-01
2    1            2010-02-01
3    1            2010-03-01
4    1            2010-06-01
5    2            2010-04-01
6    2            2010-05-01
7    2            2010-06-01
8    2            2010-07-01

I would like to produce the following result:

CustomerId    LastPaymentDateInPeriod
-------------------------------------
1             2010-03-01
2             2010-07-01

Where LastPaymentDateInPeriod is the PaymentDate with the highest value within a three-month period. If there is more than one three-month period for a given customer it would have to return the highest value from the most recent period (this is what I tried to illustrate for customer 2 in the above example). Note that three payments on three consecutive days would also meet the criteria. The payments just have to fall within a three-month period.

I know how to do this with a cursor and a lot of smaller queries but this is slow (and, I've come to understand, should only be a last resort). So do any of you SqlServer geniuses know how to do this with a query?

Thanks in advance.

Answer 1

This should do the job:

select 
    CustomerID,
    max(LastPaymentDateInPeriod) as LastPaymentDateInPeriod
from
(
    select
      LastPaymentInPeriod.CustomerID,
      LastPaymentInPeriod.PaymentDate as LastPaymentDateInPeriod
    from Payment LastPaymentInPeriod
      inner join Payment RelatedPayment on
        LastPaymentInPeriod.CustomerID = RelatedPayment.CustomerID and
        LastPaymentInPeriod.PaymentDate > RelatedPayment.PaymentDate and
        datediff(m, RelatedPayment.PaymentDate, LastPaymentInPeriod.PaymentDate) < 3
    group by
      LastPaymentInPeriod.CustomerID,
      LastPaymentInPeriod.PaymentDate
    having
      count(*) > 1

 ) as PaymentPeriods
group by
    CustomerID

update: I've tested this now and it seems to work for @Martin's data

update2: If it's a requirement that Jan 31 and Apr 1 should be considered as less than 3 months apart then the DATEDIFF function call can be replaced with something like this:

create function fn_monthspan
(
    @startdate datetime,
    @enddate datetime
)
returns int
as
begin
    return datediff(m, @startdate, @enddate) - case when datepart(d, @startdate) > datepart(d, @enddate) then 1 else 0 end
end

Answer 2

I thought of:

select customerId,max(PaymentDate) from payment where customerId in
(select case when count(*)<3 then null else customerId end as customerId from payment where paymentdate>dateadd(month,-3,getdate()) group by customerId)
group by customerId;

Answer 3

This gives you all three payments within a 3 month span.

;
WITH CustomerPayments AS
(
          SELECT 1 Id,    1 CustomerId,            Convert (DateTime, '2010-01-01') PaymentDate
    UNION SELECT 2,    1,            '2010-02-01'
    UNION SELECT 3,    1,            '2010-03-01'
    UNION SELECT 4,    1,            '2010-06-01'
    UNION SELECT 5,    2,            '2010-04-01'
    UNION SELECT 6,    2,            '2010-05-01'
    UNION SELECT 7,    2,            '2010-06-01'
    UNION SELECT 8,    2,            '2010-07-01'
    UNION SELECT 9,    3,            '2010-07-01'
    UNION SELECT 10,   3,            '2010-07-01'
),
FirstPayment AS
(
    SELECT Id, CustomerId, PaymentDate
    FROM CustomerPayments 
    where Id IN
    (
        SELECT Min (Id) Id
        FROM CustomerPayments
        Group by CustomerId
    )
),
SecondPayment AS
(
    SELECT Id, CustomerId, PaymentDate
    FROM CustomerPayments 
    where Id IN
    (
        SELECT Min (Id) Id
        FROM CustomerPayments
        WHERE ID NOT IN 
        (
            SELECT ID 
            from FirstPayment
        )
        Group by CustomerId
    )
),
ThirdPayment AS
(
    SELECT Id, CustomerId, PaymentDate
    FROM CustomerPayments 
    where Id IN
    (
        SELECT Min (Id) Id
        FROM CustomerPayments
        WHERE ID NOT IN 
        (
            SELECT ID 
            from FirstPayment
            UNION
            SELECT ID 
            from SecondPayment
        )
        Group by CustomerId
    )
)
SELECT * 
FROM 
    FirstPayment FP

    Left JOIN SecondPayment SP
        ON FP.CustomerId = SP.CustomerId

    Left JOIN ThirdPayment TP
        ON SP.CustomerId = TP.CustomerId

WHERE 1=1
    AND SP.PaymentDate IS NOT NULL
    AND TP.PaymentDate IS NOT NULL
    AND ABS (DATEDIFF (mm, SP.PaymentDate, TP.PaymentDate)) <3

Answer 4

Bit of a rushed job as I'm off out.

declare @T TABLE
(
Id int,
CustomerId int,
PaymentDate SmallDateTime
)
insert into @T
SELECT 1, 1,'2010-01-01' UNION ALL
SELECT 2, 1,'2010-02-01' UNION ALL
SELECT 3, 1,'2010-03-01' UNION ALL
SELECT 4, 1,'2010-06-01' UNION ALL
SELECT 5, 2,'2010-04-01' UNION ALL
SELECT 6, 2,'2010-05-01' UNION ALL
SELECT 7, 2,'2010-06-01' UNION ALL
SELECT 8, 2,'2010-07-01' 

;with CTE1 AS
(
SELECT Id, CustomerId, PaymentDate, ROW_NUMBER() OVER (PARTITION BY CustomerId ORDER BY PaymentDate) RN
FROM @T
),  CTE2 AS
(
SELECT  C1.Id, C1.CustomerId, MAX(C2.PaymentDate) AS LastPaymentDateInPeriod
FROM CTE1 C1 LEFT JOIN CTE1 C2 ON C1.CustomerId = C2.CustomerId AND C2.RN BETWEEN C1.RN AND C1.RN + 2  and C2.PaymentDate <=DATEADD(MONTH,3,C1.PaymentDate)
GROUP BY C1.Id, C1.CustomerId
HAVING COUNT(*)=3
)
SELECT CustomerId, MAX(LastPaymentDateInPeriod) LastPaymentDateInPeriod
FROM CTE2
GROUP BY CustomerId