SQL: count entries that are close to each others time - sql

Question

I'm trying to create a query that counts each time a task is added within 7 days of the previous time a task was created for the same piece of equipment.
We have service requests that can have multiple service tasks. Each task can have a piece of service equipment linked to it.
Here's the code as I have it so far. My results end up counting all service tasks minus one instead of just the ones that are within 7 days of a previous task and I'm not sure why. Any ideas on what I'm doing wrong?
SELECT c.CustomerID,
e.strSerialNumber,
COUNT(r2.dtmServiceRequestStartDate)
as 'Call-Backs'
FROM tblServiceRequest r2
LEFT OUTER JOIN tblServiceTask t2
ON r2.lngServiceRequestID = t2.lngServiceRequestID
LEFT OUTER JOIN tblServiceEquipment e
ON e.lngSEID = t2.lngSEID
INNER JOIN tblCustomers c
ON r2.strShipTo = c.CustomerID
WHERE r2.dtmServiceRequestStartDate < (
SELECT MAX(r.dtmServiceRequestStartDate)
FROM tblServiceRequest r
LEFT OUTER JOIN tblServiceTask t
ON r.lngServiceRequestID = t.lngServiceRequestID
WHERE r.dtmServiceRequestStartDate < (
SELECT MAX(dtmServiceRequestStartDate)
FROM tblServiceRequest r1
LEFT OUTER JOIN tblservicetask t1
ON r1.lngServiceRequestID = t1.lngServiceRequestID
WHERE t.lngSEID = t1.lngSEID)
) + 7
AND t2.lngSEID IS NOT NULL
AND c.Active = 1
GROUP BY c.CustomerID, e.strSerialNumber

Answer 1

What you are looking for is the DATEDIFF
function. Example from the MSDN:
USE AdventureWorks; GO SELECT DATEDIFF(day, OrderDate, GETDATE()) AS NumberOfDays FROM Sales.SalesOrderHeader; GO