求一sql语句？？
一数据表格：
Carid(车辆id) jydate(加油日期) jysl(加油数量) jygls(加油公里数)
A2012-06-02 30 1200
A 2012-06-12 35 1400
A 2012-06-22 32 1600
B2012-06-02 34 1200
B 2012-06-24 33 1400
按照carid 加油月份 加油数量 加油公里数 平均油耗 显示：
其中平均油耗为（月份加油数合计-按日期该月第一次加油数量）×100/加油公里数之差
比如A车六月份油耗为(35＋32)*100/(1600-1200),sql语句如何实现？
[解决办法]
--> 测试数据：[tb]IF OBJECT_ID('[tb]') IS NOT NULL DROP TABLE [tb]GOCREATE TABLE [tb]([Carid] VARCHAR(1),[jydate] DATETIME,[jysl] INT,[jygls] INT)INSERT [tb]SELECT 'A','2012-06-02',30,1200 UNION ALLSELECT 'A','2012-06-12',35,1400 UNION ALLSELECT 'A','2012-06-22',32,1600 UNION ALLSELECT 'B','2012-06-02',34,1200 UNION ALLSELECT 'B','2012-06-24',33,1400GO--> 测试语句：select a.Carid,convert(varchar(7),a.[min_jydate],120) as 月份,(sum_jysl-b.jysl)*100.0/(end_jygls-begin_jygls) as 平均油耗from( select Carid,min([jydate])as min_jydate,sum([jysl]) as sum_jysl ,min([jygls]) as begin_jygls ,max([jygls]) as end_jygls from tb group by Carid,convert(varchar(7),[jydate],120)) ajoin tb as b on a.Carid=b.Carid and a.min_jydate=b.jydate/*Carid 月份 平均油耗----- ------- ---------------------------------------A 2012-06 16.750000000000B 2012-06 16.500000000000(2 行受影响)*/