Please help me with the group by clause - sql

Question

USE [MAS_CAN]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[spHistorybyCalenderYear]--create a stored proc
#Year int = '2013'
AS
Begin
SET NOCOUNT ON
SELECT
isnull(round(l.UnitPrice*l.QuantityShipped,2),0) as SalesAmount,
isnull(round(l.unitCost*l.QuantityShipped,2),0) as CostAmount,
(case
when month(h.INVOICEDATE)=01 then '01'
when month(h.INVOICEDATE)=02 then '02'
when month(h.INVOICEDATE)=03 then '03'
when month(h.INVOICEDATE)=04 then '04'
when month(h.INVOICEDATE)=05 then '05'
when month(h.INVOICEDATE)=06 then '06'
when month(h.INVOICEDATE)=07 then '07'
when month(h.INVOICEDATE)=08 then '08'
when month(h.INVOICEDATE)=09 then '09'
when month(h.INVOICEDATE)=10 then '10'
when month(h.INVOICEDATE)=11 then '11'
when month(h.INVOICEDATE)=12 then '12'
END) as Period
FROM AR_INVOICEHISTORYHEADER h join AR_INVOICEHISTORYDETAIL l on (h.INVOICENO = l.INVOICENO)
Group by l.unitprice,l.unitcost,l.quantityShipped,h.invoicedate
order by Period
END
I would like to group it by period...Say I would like to see
Period SalesAmount CostAmount
01 22 19
02 24 25

Answer 1

Use this:
GROUP BY l.unitprice, l.unitcost, l.quantityShipped, CAST(MONTH(h.invoicedate) as varchar)
Also, you can get rid of that large case statement if you use this in its place:
SELECT
isnull(round(l.UnitPrice*l.QuantityShipped,2),0) as SalesAmount,
isnull(round(l.unitCost*l.QuantityShipped,2),0) as CostAmount,
CAST(MONTH(h.invoicedate) as varchar) as Period
FROM ...
As #Kaf mentioned, if you want Period to be 0 padded you can use either of these instead of the direct CAST:
right(100 + month(h.invoicedate),2)
left(convert(varchar, h.invoicedate, 10), 2)