数据库表里有这么几个字段，日期，最高温度，最低温度
日期是精确到天的
现在有这么个需求，要按月和年去查最高温度和最低温度，
现在录的数据都是按天录的，要按月去得到每月的平均最高温度和最低温度
我实在是想不出来了。。。求大家帮帮忙
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按月:
select * from test a where a.最高温度=(select max(最高温度) from test b
where month(a.日期)=month(b.日期))
按年:
select * from test a where a.最高温度=(select max(最高温度) from test b
where year(a.日期)=year(b.日期))
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还有种最笨的方法，就是把日期转换成字符串，通过like筛选...
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呃，这个得看你想得到的结果是以什么方式查询，如果是单月每个去查的话相当好写。。。
select avg(最高温度),avg(最低温度)
from 表
where 日期>=月第一天 and 日期<=月最后一天
如果是想一下全年的都出来的话可以先把日期转换成年月格式的字符串，然后做为条件group 同样使用AVG函数就成，貌似也不是很困难，顶多需要先构建出结果集来
select avg(最高温度),avg(最低温度)
from (select convert(varchar(7), 日期,20) as 月,最高温度,最低温度 from 表) a
group by a.月
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- SQL code
if OBJECT_ID('test')is not nulldrop table testgocreate table test(日期 date,最高温度 int,最低温度 int)goinsert test select '2012-01-01',7,-5 union allselect '2012-01-02',6,-8 union allselect '2012-01-03',6,-7 union allselect '2012-01-04',8,0 union allselect '2012-01-05',9,1 union allselect '2012-02-01',12,2 union allselect '2012-02-02',14,3 union allselect '2012-02-03',10,1 union allselect '2012-02-04',11,0 union allselect '2012-02-05',13,2 union allselect '2012-03-01',15,6 union allselect '2012-03-02',17,8 union allselect '2012-03-03',16,6 union allselect '2012-03-04',14,5select *,AVG(最高温度)over(partition by month(日期)) as 月平均最高温度,AVG(最低温度)over(partition by month(日期)) as 月平均最低温度from test/*日期 最高温度 最低温度 月平均最高温度 月平均最低温度------------------------------------2012-01-01 7 -5 7 -32012-01-02 6 -8 7 -32012-01-03 6 -7 7 -32012-01-04 8 0 7 -32012-01-05 9 1 7 -32012-02-01 12 2 12 12012-02-02 14 3 12 12012-02-03 10 1 12 12012-02-04 11 0 12 12012-02-05 13 2 12 12012-03-01 15 6 15 62012-03-02 17 8 15 62012-03-03 16 6 15 62012-03-04 14 5 15 6*/
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- SQL code
create table test11(dt datetime,high float,low float)insert into test11 values('2012-01-01',25.1,5.2)insert into test11 values('2012-01-03',35.1,5.2)insert into test11 values('2012-01-04',15.1,5.2)insert into test11 values('2012-01-05',25.1,11.2)insert into test11 values('2012-01-09',25.1,12.2)insert into test11 values('2012-02-01',35.1,13.2)insert into test11 values('2012-02-02',35.1,22.2)insert into test11 values('2012-02-03',25.1,18.2)insert into test11 values('2012-02-04',25.1,13.2)select CONVERT(char(7),dt,23),SUM(high)/COUNT(*),SUM(low)/COUNT(*) from test11group by CONVERT(char(7),dt,23)select CONVERT(char(4),dt,23),SUM(high)/COUNT(*),SUM(low)/COUNT(*) from test11group by CONVERT(char(4),dt,23)drop table test11
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- SQL code
if OBJECT_ID('test')is not nulldrop table testgocreate table test(日期 date,最高温度 int,最低温度 int)goinsert test select '2012-01-01',7,-5 union allselect '2012-01-02',6,-8 union allselect '2012-01-03',6,-7 union allselect '2012-01-04',8,0 union allselect '2012-01-05',9,1 union allselect '2012-02-01',12,2 union allselect '2012-02-02',14,3 union allselect '2012-02-03',10,1 union allselect '2012-02-04',11,0 union allselect '2012-02-05',13,2 union allselect '2012-03-01',15,6 union allselect '2012-03-02',17,8 union allselect '2012-03-03',16,6 union allselect '2012-03-04',14,5--SQL Server 2000select *,(select AVG(最高温度) from test b where convert(varchar(7),a.日期,120)=convert(varchar(7),b.日期,120)) as 月平均最高温度,(select AVG(最低温度) from test c where convert(varchar(7),a.日期,120)=convert(varchar(7),c.日期,120)) as 月平均最低温度from test a/*日期 最高温度 最低温度 月平均最高温度 月平均最低温度-----------------------------------2012-01-01 7 -5 7 -32012-01-02 6 -8 7 -32012-01-03 6 -7 7 -32012-01-04 8 0 7 -32012-01-05 9 1 7 -32012-02-01 12 2 12 12012-02-02 14 3 12 12012-02-03 10 1 12 12012-02-04 11 0 12 12012-02-05 13 2 12 12012-03-01 15 6 15 62012-03-02 17 8 15 62012-03-03 16 6 15 62012-03-04 14 5 15 6*/--9楼说的那不是重点