Question

Im having a problem with derived columns in SSIS. When in SSMS i can set a column to have a default value using the following code:

(dateadd(month,datediff(month,(0),getdate())-(1),(0)))

and when data is entered into the database it will give it the timestamp of the previous month in the following format for example:

 2010-09-01 00:00:00.000

This strangely is what im looking for and trying to duplicate/produce similar using the Derived Column DFT.

So far i have:

DATEADD("mm",DATEDIFF("mm",GETDATE(),GETDATE()) - 1,GETDATE())

which produces the month succesfully but the GETDATE() is not a correct replacement for the 0’s in the original code.

Does the 0’s in the original code signify the start date in SQL?

Any help would be much appreciated.

Regards,

Lee

Answer 1

Here’s what I think you may be looking for. It is an SSIS expression that gets the first day of the previous month for a given day (GETDATE() in the example).

DATEADD("mm",DATEDIFF("mm", (DT_DBTIMESTAMP)2, GETDATE()) - 1, (DT_DBTIMESTAMP)2)

I tried to simulate your SQL version of the expression, which determined the number of months between the 0 datetime and the current datetime. And, then it added the number of months to the 0 datetime.

It’s not too important what the 0 datetime is, except that you wanted the 1st day of the month. In SQL the 0 datetime is 1900-01-01 00:00:00.000, so adding months automatically gives you the first day of the month. In SSIS expressions, the 0 datetime is 1899-12-30 00:00:00.000. Since you want the first day of a month, the expression above refers to the 2 datetime. So, in the expression (DT_DBTIMESTAMP)2 casts the number 2 to 1900-01-01 00:00:00.000.