select 年度,季度 ,sum(订购数量) as 订购数量 from (

SELECT YEAR(订单.订购日期) AS 年度,

(CASE

WHEN MONTH(订单.订购日期) IN (1,2,3) THEN '1'

WHEN MONTH(订单.订购日期) IN (4,5,6) THEN '2'

WHEN MONTH(订单.订购日期) IN (7,8,9) THEN '3' ELSE '4' END) AS 季度,

订单明细.数量 AS 订购数量

FROM 订单

LEFT JOIN 订单明细 ON 订单明细.订单ID = 订单.订单ID ) a    

GROUP BY 年度,季度    

ORDER BY 年度,季度

改成下面的试试

select * from

(SELECT YEAR(订单.订购日期) AS 年度,

(CASE

WHEN MONTH(订单.订购日期) IN (1,2,3) THEN '1'

WHEN MONTH(订单.订购日期) IN (4,5,6) THEN '2'

WHEN MONTH(订单.订购日期) IN (7,8,9) THEN '3' ELSE '4' END) AS 季度,

SUM(订单明细.数量) AS 订购数量

FROM 订单

LEFT JOIN 订单明细 ON 订单明细.订单ID = 订单.订单ID)     

GROUP BY 年度,季度    

ORDER BY 年度,季度

==================

SELECT YEAR(订单.订购日期) AS 年度,

(CASE

WHEN MONTH(订单.订购日期) IN (1,2,3) THEN '1'

WHEN MONTH(订单.订购日期) IN (4,5,6) THEN '2'

WHEN MONTH(订单.订购日期) IN (7,8,9) THEN '3' ELSE '4' END) AS 季度,

SUM(订单明细.数量) AS 订购数量

FROM 订单

LEFT JOIN 订单明细 ON 订单明细.订单ID = 订单.订单ID     

GROUP BY

 YEAR(订单.订购日期) ,

(CASE

WHEN MONTH(订单.订购日期) IN (1,2,3) THEN '1'

WHEN MONTH(订单.订购日期) IN (4,5,6) THEN '2'

WHEN MONTH(订单.订购日期) IN (7,8,9) THEN '3' ELSE '4' END)

ORDER BY 1,2