Overlapping Date Ranges - Identifying Only the Overlap

Question

I\'ve seen a lot of solutions to identify records where date ranges overlap, and still other examples of merging overlapping ranges.

However I am interested in results

Answer 1

CREATE TABLE #TMP
(
    CustomerID INT,
    ProductID VARCHAR(12),
    Eff_Dt DATE,
    End_Dt DATE
);
--
INSERT INTO #TMP
VALUES
-- Customer 1000: Expecting results to show 2 rows: "1/1 - 1/5"; "1/10 - 1/15"
(1000, 'PRODUCT_A', N'2013-01-01T00:00:00', N'2013-01-31T00:00:00'),
(1000, 'PRODUCT_B', N'2013-01-01T00:00:00', N'2013-01-05T00:00:00'),
(1000, 'PRODUCT_B', N'2013-01-10T00:00:00', N'2013-01-15T00:00:00'),
(1000, 'PRODUCT_C', N'2013-01-01T00:00:00', N'2013-01-31T00:00:00'),
-- Customer 2000: Expecting results to show 1 row: "1/19 - 1/31"
(2000, 'PRODUCT_A', N'2013-01-01T00:00:00', N'2013-01-31T00:00:00'),
(2000, 'PRODUCT_B', N'2013-01-01T00:00:00', N'2013-01-31T00:00:00'),
(2000, 'PRODUCT_C', N'2013-01-19T00:00:00', N'2013-01-31T00:00:00'),
-- Customer 3000: Expecting results to show NO rows (or nulls)
(3000, 'PRODUCT_A', N'2013-01-01T00:00:00', N'2013-01-10T00:00:00'),
(3000, 'PRODUCT_A', N'2013-01-16T00:00:00', N'2013-01-31T00:00:00'),
(3000, 'PRODUCT_B', N'2013-01-01T00:00:00', N'2013-01-12T00:00:00'),
(3000, 'PRODUCT_C', N'2013-01-15T00:00:00', N'2013-01-31T00:00:00'),
-- Customer 4000: Expecting results to show 1 row: "1/15 - 1/23"
(4000, 'PRODUCT_A', N'2013-01-15T00:00:00', N'2013-01-31T00:00:00'),
(4000, 'PRODUCT_B', N'2013-01-01T00:00:00', N'2013-01-31T00:00:00'),
(4000, 'PRODUCT_C', N'2013-01-01T00:00:00', N'2013-01-23T00:00:00'),
-- Customer 5000: Expecting results to show 0 rows
(5000, 'PRODUCT_A', N'2013-01-17T00:00:00', N'2013-01-31T00:00:00'),
(5000, 'PRODUCT_B', N'2013-01-01T00:00:00', N'2013-01-10T00:00:00'),
(5000, 'PRODUCT_C', N'2013-01-07T00:00:00', N'2013-01-19T00:00:00'),
-- Customer 6000: Expecting results to show 3 rows: "1/11 - 1/12"; "1/17 - 1/22"; "1/26 - 1/27"
(6000, 'PRODUCT_A', N'2013-01-01T00:00:00', N'2013-01-04T00:00:00'),
(6000, 'PRODUCT_A', N'2013-01-09T00:00:00', N'2013-01-12T00:00:00'),
(6000, 'PRODUCT_A', N'2013-01-17T00:00:00', N'2013-01-22T00:00:00'),
(6000, 'PRODUCT_A', N'2013-01-26T00:00:00', N'2013-01-31T00:00:00'),
(6000, 'PRODUCT_B', N'2013-01-04T00:00:00', N'2013-01-28T00:00:00'),
(6000, 'PRODUCT_C', N'2013-01-11T00:00:00', N'2013-01-27T00:00:00');
--
--
;
WITH MIN_MAX
AS (SELECT MIN(Eff_Dt) S,
           MAX(End_Dt) E
    FROM #TMP),
     ALL_DATES
AS (SELECT MIN_MAX.S DT
    FROM MIN_MAX
    UNION ALL
    SELECT DATEADD(DAY, 1, ALL_DATES.DT)
    FROM ALL_DATES
    WHERE ALL_DATES.DT < (SELECT MIN_MAX.E FROM MIN_MAX)),
     GROUPED
AS (SELECT Q.CustomerID,
           Q.ProductID,
           Q.DT,
           CASE WHEN MAX(TX.CustomerID) IS NULL THEN 0 ELSE 1 END YES
    FROM
    (
        SELECT *FROM ALL_DATES
            CROSS JOIN
            (SELECT DISTINCT CustomerID, ProductID FROM #TMP) AS AQ
    ) AS Q
        LEFT JOIN #TMP AS TX
            ON TX.CustomerID = Q.CustomerID
               AND TX.ProductID = Q.ProductID
               AND Q.DT
               BETWEEN TX.Eff_Dt AND TX.End_Dt
    GROUP BY Q.CustomerID,
             Q.ProductID,
             Q.DT),
     BuildFlags
AS (SELECT G.CustomerID,
           G.DT,
           ROW_NUMBER() OVER (PARTITION BY G.CustomerID ORDER BY G.DT) RN,
           CASE
               WHEN WQ.tot =
               (
                   SELECT COUNT(DISTINCT g2.ProductID)
                   FROM GROUPED AS g2
                   WHERE g2.CustomerID = G.CustomerID
                         AND g2.DT = G.DT
                         AND g2.YES = 1
               ) THEN 1
               ELSE 0
           END FLAG
    FROM GROUPED AS G
        CROSS APPLY
    (
        SELECT COUNT(DISTINCT E9.ProductID) tot
        FROM #TMP AS E9
        WHERE E9.CustomerID = G.CustomerID
    ) AS WQ ),
     AddRanks
AS (SELECT *,
           BuildFlags.RN - ROW_NUMBER() OVER (PARTITION BY BuildFlags.CustomerID,
                                                           BuildFlags.FLAG
                                              ORDER BY BuildFlags.DT
                                             ) groupRank
    FROM BuildFlags)
SELECT AddRanks.CustomerID,
       MIN(AddRanks.DT) AS StartDate,
       MAX(AddRanks.DT) AS EndDate
FROM AddRanks
WHERE AddRanks.FLAG = 1
GROUP BY AddRanks.CustomerID,
         AddRanks.groupRank
ORDER BY AddRanks.CustomerID,
         MIN(AddRanks.DT)
OPTION (MAXRECURSION 0);

You can Find the Execution at DB Fiddle