Question

Given a start date and an end date, I need a count of instances between those two dates. So given the following:

Table:

Col 1   Start_Date    End_Date

1       01/01/2010    02/01/2010  
2       01/01/2010    04/01/2010  
3       03/01/2010    04/01/2010  
4       03/01/2010    04/01/2010

If I was looking between the 1st (01/01) and the 2nd (02/01) I would expect a count of 2. If I was looking for the 3rd to the 4th I would expect a count of 3. If I was looking across the whole date range then I would expect a count of 4. Make sense?

NOTE: The dates are already converted to midnight, no code needs to be added for this. Also, dates are in dd/MM/yyyy format throughout this question.

Currently I have something similar to the following:

SELECT COUNT(*), Group_Field
FROM MY_Table
WHERE Start_Date < DATEADD(DAY, 1, @StartDate) AND End_Date > @EndDate
GROUP BY Group_Field

I did at some point think that this was right, but i’m not convinced now…

I did previously have:

WITH Dates AS ( 
            SELECT [Date] = @StartDate
            UNION ALL SELECT [Date] = DATEADD(DAY, 1, [Date])
            FROM Dates WHERE [Date] < @EndDate
) 

SELECT COUNT(*), Group_Field -- In this case it is [Date]
FROM MY_Table
CROSS APPLY Dates
WHERE Start_Date < DATEADD(DAY, 1, @StartDate) AND End_Date > [Date]
GROUP BY Group_Field

But I am not sure that I am using CROSS APPLY properly in this case…

The questions:

1) Am I using Cross Apply right in the 2nd example (and the CTE for that matter)?
2) If so, which logic is right? (I think it’s the 2nd)

/Discuss 🙂

Answer 1

The solution ended up being:

WHERE [Date] BETWEEN Start_Date AND DATEADD(Day, -1, End_Date)