如何做本月最大与上月最大值之差的查询？

roych

查两个max，减一下不就得了么？

1. select A.月份,B.当月最大-A.当月最大 as 差额 from
   
2. (SELECT Max(表1.数量) AS 当月最大, Month([日期]) AS 月份
   
3. FROM 表1
   
4. GROUP BY Month([日期])) AS A
   
5. left join(
   
6. SELECT Max(表1.数量) AS 当月最大, Month([日期])-1 AS 月份
   
7. FROM 表1
   
8. GROUP BY Month([日期])) AS B
   
9. on A.月份=B.月份

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