SSIS Using Derived column to reference column from same table
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Ok what I am trying to do is import an xls spreadsheet into a table but one of the columns needs to derived from a different column in the same table. I would like to be able to do this during the import phase rather then creating a SQL Task to do it after the import. I am horrible when it comes to creating expressions in SSIS so this is probably an easy task but I just can't get it right. 

    DATEADD(s,-1,DATEADD(mm, DATEDIFF(m,0,columndata)+1,0))

That is the expression that I am trying to use. 