Question

I have a table stored on a SQL Server 2008, that associate a value to a date range.

DateFrom      DateTo         Value
2012-01-01    2012-02-01      10
2012-02-02    2012-02-15      15

The application that deal with this table, can insert a new range between the existings.
For example, If i insert

DateFrom      DateTo         Value
2012-02-07    2012-02-10      12

The result must be

DateFrom      DateTo         Value
2012-01-01    2012-02-01      10
2012-02-02    2012-02-06      15
2012-02-07    2012-02-10      12
2012-02-11    2012-02-15      15

I can do that programmatically from the application, but I wonder if there is some fast SQL statement that make me able to set the data values by referencing other row’s field and performing data operation on it.

A MUST requirement is that the date range must represent a time sequence, two range cannot span each other.

Answer 1

I’ve had similar problems in the past, and found that if the range needs to be continuous the best approach is to do away with the End Date of the range, and calculate this as the Next start date. Then if needs be create a view as follows:

SELECT  FromDate,
        (   SELECT  DATEADD(DAY, -1, MIN(DateFrom))
            FROM    YourTable b
            WHERE   b.FromDate > a.FromDate
        ) [ToDate],
        Value
FROM    YourTable a

This ensures that 2 ranges can never cross, however does not necessarily ensure no work is required upon insert to get the desired result, but it should be more maintainable and have less scope for error than storing both the start and end date.

ADDENDUM

Once I had written out all of the below I realised it does not improve maintainability that much to do away with the DateTo Field, it still requires a fair amount of code for the validation, but here’s how I would do it anyway.

DECLARE  @T table (DateFrom DATE, Value INT)
INSERT INTO @T VALUES ('20120101', 10), ('20120202', 15), ('20120207', 12), ('20120211', 15)

DECLARE @NewFrom DATE = '20120209',
        @NewTo DATE = '20120210',
        @NewValue INT = 8

-- SHOW INITIAL VALUES FOR DEMONSTATIVE PURPOSES -- 
SELECT  DateFrom,
        ISNULL((   SELECT  DATEADD(DAY, -1, MIN(DateFrom))
                    FROM    @t b
                    WHERE   b.DateFrom > a.DateFrom
                ), CAST(GETDATE() AS DATE)) [DateTo],
        Value
FROM    @t a
ORDER BY DateFrom

;WITH CTE AS
(   SELECT  DateFrom,
            (   SELECT  DATEADD(DAY, -1, MIN(DateFrom))
                FROM    @t b
                WHERE   b.DateFrom > a.DateFrom
            ) [DateTo],
            Value
    FROM    @t a    
), 
MergeCTE AS
(   SELECT  @NewFrom [DateFrom], @NewValue [Value], 'INSERT' [RowAction]
    WHERE   @NewFrom < @NewTo   -- ENSURE A VALID RANGE IS ENTERED
    UNION ALL 
    -- INSERT A ROW WHERE THE NEW DATE TO SLICES AN EXISTING PERIOD
    SELECT  DATEADD(DAY, 1, @NewTo), Value, 'INSERT'
    FROM    CTE
    WHERE   @NewTo BETWEEN DateFrom AND DateTo
    UNION ALL 
    -- DELETE ALL ENTRIES STARTING WITHIN THE DEFINED PERIOD
    SELECT  DateFrom, Value, 'DELETE'
    FROM    CTE
    WHERE   DateFrom BETWEEN @NewFrom AND @NewTo
)
MERGE INTO @t t USING MergeCTE c ON t.DateFrom = c.DateFrom AND t.Value = c.Value
WHEN MATCHED AND RowAction = 'DELETE' THEN DELETE
WHEN NOT MATCHED THEN INSERT VALUES (c.DateFrom, c.Value);

SELECT  DateFrom,
        ISNULL((   SELECT  DATEADD(DAY, -1, MIN(DateFrom))
                    FROM    @t b
                    WHERE   b.DateFrom > a.DateFrom
                ), CAST(GETDATE() AS DATE)) [DateTo],
        Value
FROM    @t a
ORDER BY DateFrom