SqlServer Divide Date Range

SELECT 
  CASEWHEN BeginDate > MonthStart THEN BeginDate ELSE MonthStart ENDAS BeginDate, 
  CASEWHEN EndDate   < MonthEnd   THEN EndDate   ELSE MonthEnd   ENDAS EndDate, 
  …  /* other columns as needed */ 
FROM( 
  SELECT 
    d.*,  /* or you could be more specific here */ 
    ( 
      DATEADD(month, DATEDIFF(month,0, d.BeginDate)+ v.number,0) 
    )AS MonthStart, 
    DATEADD(day,-1, 
      DATEADD(month, DATEDIFF(month,0, d.BeginDate)+ v.number +1,0) 
    )AS MonthEnd 
  FROM RowsOfData d 
    INNERJOIN master..spt_values v ON v.type ='P' 
      AND v.number BETWEEN0AND DATEDIFF(month, d.BeginDate, d.EndDate) 
) s