Question

I’m looking for a solution where I have to create a set of records from one record using data from another table. The table definition:

DECLARE A AS TABLE
(
 AID BIGINT NOT NULL,
 StartDate DATETIME NOT NULL,
 EndDate DATETIME
)

DECLARE B AS TABLE
(
 AID BIGINT NOT NULL,
 StartDate DATETIME NOT NULL,
 EndDate DATETIME NULL
)

The idea is that when A contains:

1 | 01-01-2010 | 01-02-2010
2 | 01-10-2010 | 31-10-2010

and B contains:

1 | 01-01-2010 | 15-01-2010
2 | 15-10-2010 | 20-10-2010

we recieve 5 records:

1 | 01-01-2010 | 15-01-2010
1 | 16-01-2010 | 01-02-2010
2 | 01-10-2010 | 15-10-2010
2 | 16-10-2010 | 20-10-2010
2 | 21-10-2010 | 31-10-2010

Currently we do this with a cursor on A and an inner loop cursor on B, we have to do this in SQLServer (TSQL or in worst case CLR)

Any ideas on how to write this as a select so that the overhead of the cursor disappears?

Answer 1

DECLARE @A TABLE (AID BIGINT NOT NULL, StartDate DATETIME NOT NULL, EndDate DATETIME)
DECLARE @B TABLE (AID BIGINT NOT NULL, StartDate DATETIME NOT NULL, EndDate DATETIME NULL)

SET DATEFORMAT dmy
INSERT @A VALUES (1 ,'01-01-2010','01-02-2010')
INSERT @A VALUES (2 ,'01-10-2010','31-10-2010')
INSERT @B VALUES (1 ,'01-01-2010','15-01-2010')
INSERT @B VALUES (2 ,'15-10-2010','20-10-2010')

;WITH transitions as
(
    SELECT *, ROW_NUMBER() OVER (PARTITION BY AID ORDER BY startdate) Sequence
    FROM (
        SELECT A.AID, A.startdate
        FROM @a A
        UNION
        SELECT A.AID, B.startdate + 1
        FROM @A A
        INNER JOIN @b B ON B.startdate > A.startdate AND B.startdate < A.enddate
        UNION
        SELECT A.AID, B.enddate + 1
        FROM @A A
        INNER JOIN @b B ON B.enddate > A.startdate AND B.enddate < A.enddate
        UNION
        SELECT A.AID, A.enddate + 1
        FROM @a A
        WHERE A.enddate > A.startdate
    ) T
)   
SELECT T1.AID, T1.startdate startdate, T2.startdate - 1 enddate
FROM transitions T1
INNER JOIN transitions T2 ON T2.AID = T1.AID AND T2.Sequence = T1.Sequence + 1
ORDER BY T1.AID, T1.Sequence