Question

this one has me stuck fast.

Data:

Month           Total         Impact    Forecast
------------------------------------------------
2010-04-01    45792.0000    1.0000    NULL
2010-05-01    51789.0000    1.0000    NULL
2010-06-01    58228.0000    1.0000    NULL
2010-07-01    52956.5217    1.0000    NULL
2010-08-01    53600.4700    0.8810    NULL
2010-09-01    54257.8784    1.1838    NULL
2010-10-01    55134.0669    1.0000    NULL 

Now what I’m trying to do is loop through the current contents of the table and update the Forecast column using conditional IF statements as follows:

If Impact = 1.0000 then forecast = (current month) total * Impact
If Impact < 1.0000 then forecast = (month -1) total * Impact
If Impact > 1.0000 then forecast = (month -2) total * Impact

I did think of using the CASE statement though calculating the forecast using previous dates stumped me, I presume I will need to utilise a while statements and RBAR.

Much appreciated.

Answer 1

How about this:

UPDATE [Table]
SET
    [Forecast] = [Impact] * CASE
        WHEN [Impact] = 1.0000 THEN
        (
            SELECT
                [InnerTable].[Total]
            FROM [Table] AS [InnerTable]
            WHERE [InnerTable].[Month] = [Table].[Month]
        )
        WHEN [Impact] < 1.0000 THEN
        (
            SELECT
                [InnerTable].[Total]
            FROM [Table] AS [InnerTable]
            WHERE [InnerTable].[Month] = DATEADD(month, -1, [Table].[Month])
        )
        ELSE
        (
            SELECT
                [InnerTable].[Total]
            FROM [Table] AS [InnerTable]
            WHERE [InnerTable].[Month] = DATEADD(month, -2, [Table].[Month])
        )
    END    
FROM [Table]