Question

I have a BreakdownLog table with the following columns:

EquipmentID, ProblemID, BreakdownDate, IssueFixedDate

Each equipment can have multiple breakdowns, and more importantly, there could be overlapping date ranges for the same equipment!

For example, given below data:

EquipmentID|ProblemID|BreakdownDate|IssueFixedDate
1          |1        |01-Jun-2011  |01-Sep-2011
1          |2        |01-Jun-2011  |01-Oct-2011
2          |1        |01-Jun-2011  |01-Oct-2011
2          |2        |01-Jun-2011  |01-Oct-2011
3          |1        |15-Jun-2011  |01-Sep-2011
3          |2        |10-Jun-2011  |25-Aug-2011
4          |1        |01-Jun-2011  |01-Aug-2011
4          |2        |10-Sep-2011  |22-Oct-2011
5          |1        |01-Jun-2011  |15-Jun-2011
5          |2        |02-Jun-2011  |NULL

Now I want a query which can compute the number of days each equipment was defunct. If IssueFixedDate is NULL, we assume that the equipment is still defunct and therefore compute Defunct days upto current date.

The expected result set should be:

EquipmentID|DefunctDays
1          |122
2          |122
3          |83
4          |103
5          |143

I am using SQL Server 2008. So even CTEs, cursors etc are acceptable.

Thanks
Raghu

Answer 1

This uses master..spt_values as an adhoc auxiliary numbers table. You can create your own dedicated numbers table using one of the techniques here (start the numbering at zero)

;WITH Numbers
     AS (SELECT number
         FROM   master..spt_values
         WHERE  type = 'P')
SELECT EquipmentID,
       COUNT(DISTINCT number + DATEDIFF(DAY,0, BreakdownDate)) - 1 AS DefunctDays
FROM   BreakdownLog
       JOIN Numbers N
         ON number <= DATEDIFF(DAY, BreakdownDate,
                      ISNULL(IssueFixedDate, GETDATE()))
GROUP  BY EquipmentID