SQL to find time elapsed from multiple overlapping intervals

Question

Not using MSSQL or DB2 or Oracle. No CTE. No OVERLAP predicate. No INTERVAL data type. The situation: on a vehicle to be repaired work can not start until all parts orde

Answer 1

I couldn't get @Alex W's queries to work. It is not standard SQL, so it required a lot of rewrite to be compatible with SQL Server (which I can test). But it did give me some inspiration, which I have expanded upon.

---

Find all start-points of every period of uninterrupted waiting:

SELECT DISTINCT
    t1.ID,
    t1.d1 AS date,
    -DATEDIFF(DAY, (SELECT MIN(d1) FROM Orders), t1.d1) AS n
FROM Orders t1
LEFT JOIN Orders t2                   -- Join for any events occurring while this
    ON t2.ID = t1.ID                  -- is starting. If this is a start point,
    AND t2.d1 <> t1.d1                -- it won't match anything, which is what
    AND t1.d1 BETWEEN t2.d1 AND t2.d2 -- we want.
GROUP BY t1.ID, t1.d1, t1.d2
HAVING COUNT(t2.ID) = 0

And the equivalent for end-points:

SELECT DISTINCT
    t1.ID,
    t1.d2 AS date,
    DATEDIFF(DAY, (SELECT MIN(d1) FROM Orders), t1.d2) AS n
FROM Orders t1
LEFT JOIN Orders t2
    ON t2.ID = t1.ID
    AND t2.d2 <> t1.d2
    AND t1.d2 BETWEEN t2.d1 AND t2.d2
GROUP BY t1.ID, t1.d1, t1.d2
HAVING COUNT(t2.ID) = 0

n is the number of days since some common point in time. Start-points have a negative value, and end-points have a positive value. This is so that we can just add them up to get the number of days in between.

span = end - start
span = end + (-start)
span1 + span2 = end1 + (-start1) + end2 + (-start2)

Finally, we just need to add things up:

SELECT ID, SUM(n) AS hold_days
FROM (
   SELECT DISTINCT
       t1.id,
       t1.d1 AS date,
       -DATEDIFF(DAY, (SELECT MIN(d1) FROM Orders), t1.d1)  AS n
   FROM Orders t1
   LEFT JOIN Orders t2
      ON t2.ID = t1.ID
      AND t2.d1 <> t1.d1
      AND t1.d1 BETWEEN t2.d1 AND t2.d2
   GROUP BY t1.ID, t1.d1, t1.d2
   HAVING COUNT(t2.ID) = 0
   UNION ALL
   SELECT DISTINCT
       t1.id,
       t1.d2 AS date,
       DATEDIFF(DAY, (SELECT MIN(d1) FROM Orders), t1.d2) AS n
   FROM Orders t1
   LEFT JOIN Orders t2
      ON t2.ID = t1.ID
      AND t2.d2 <> t1.d2
      AND t1.d2 BETWEEN t2.d1 AND t2.d2
   GROUP BY t1.ID, t1.d1, t1.d2
   HAVING COUNT(t2.ID) = 0
   ORDER BY ID, date
) s
GROUP BY ID;

Input table (Orders):

ID   d1           d2
 1   2011-08-01   2011-08-08
 1   2011-08-02   2011-08-06
 1   2011-08-03   2011-08-10
 1   2011-08-12   2011-08-14
 2   2011-08-01   2011-08-03
 2   2011-08-02   2011-08-06
 2   2011-08-05   2011-08-09

Output:

ID   hold_days
 1          11
 2           8

---

Alternatively, you can do this with a stored procedure.

CREATE PROCEDURE CalculateHoldTimes
    @ID int = 0
AS
BEGIN
    DECLARE Events CURSOR FOR
    SELECT *
    FROM (
        SELECT d1 AS date, 1 AS diff
        FROM Orders
        WHERE ID = @ID
        UNION ALL
        SELECT d2 AS date, -1 AS diff
        FROM Orders
        WHERE ID = @ID
    ) s
    ORDER BY date;

    DECLARE @Events_date date,
            @Events_diff int,
            @Period_start date,
            @Period_accum int,
            @Total_start date,
            @Total_count int;

    OPEN Events;

    FETCH NEXT FROM Events
    INTO @Events_date, @Events_diff;

    SET @Period_start = @Events_date;
    SET @Period_accum = 0;
    SET @Total_start = @Events_date;
    SET @Total_count = 0;

    WHILE @@FETCH_STATUS = 0
    BEGIN
        SET @Period_accum = @Period_accum + @Events_diff;

        IF @Period_accum = 1 AND @Events_diff = 1
            -- Start of period
            SET @Period_start = @Events_date;
        ELSE IF @Period_accum = 0 AND @Events_diff = -1
            -- End of period
            SET @Total_count = @Total_count +
                DATEDIFF(day, @Period_start, @Events_date);

        FETCH NEXT FROM Events
        INTO @Events_date, @Events_diff;
    END;

    SELECT
        @Total_start AS d1,
        @Events_date AS d2,
        @Total_count AS hold_time;
END;

Call it with:

EXEC CalculateHoldTimes 1;