select sum(A.amount) from A left join B on B.Aid = A.Aid where A code = xxx.(固定值)
select count(*) from B where B.Aid = A.Aid and A.Aid = xxx(固定值)
相同的A.code有两条，从B表能查出有相同A.Aid的数据为7条。当我做sum（A.amount）的时候会是7个A.amount的和。但是我只想要A.code = XXX的A.amount的和，而且这个A.amount只有两个。
不知道我说的清楚不，其实就是left join的时候关联出来7条数据，sum的时候把这7条相加了。而我想要的只是A.code = xxx的那两条记录的amount和。
求帮忙。。。。
------解决方案--------------------
- SQL code
--行列互转/******************************************************************************************************************************************************以学生成绩为例子，比较形象易懂整理人：中国风(Roy)日期:2008.06.06******************************************************************************************************************************************************/--1、行互列--> --> (Roy)生成測試數據 if not object_id('Class') is null drop table ClassGoCreate table Class([Student] nvarchar(2),[Course] nvarchar(2),[Score] int)Insert Classselect N'张三',N'语文',78 union allselect N'张三',N'数学',87 union allselect N'张三',N'英语',82 union allselect N'张三',N'物理',90 union allselect N'李四',N'语文',65 union allselect N'李四',N'数学',77 union allselect N'李四',N'英语',65 union allselect N'李四',N'物理',85 Go--2000方法:动态:declare @s nvarchar(4000)set @s=''Select @s=@s+','+quotename([Course])+'=max(case when [Course]='+quotename([Course],'''')+' then [Score] else 0 end)'from Class group by[Course]exec('select [Student]'+@s+' from Class group by [Student]')生成静态:select [Student], [数学]=max(case when [Course]='数学' then [Score] else 0 end), [物理]=max(case when [Course]='物理' then [Score] else 0 end), [英语]=max(case when [Course]='英语' then [Score] else 0 end), [语文]=max(case when [Course]='语文' then [Score] else 0 end) from Class group by [Student]GO动态:declare @s nvarchar(4000)Select @s=isnull(@s+',','')+quotename([Course]) from Class group by[Course]exec('select * from Class pivot (max([Score]) for [Course] in('+@s+'))b')生成静态:select * from Class pivot (max([Score]) for [Course] in([数学],[物理],[英语],[语文]))b生成格式:/*Student 数学 物理 英语 语文------- ----------- ----------- ----------- -----------李四 77 85 65 65张三 87 90 82 78(2 行受影响)*/------------------------------------------------------go--加上总成绩(学科平均分)--2000方法:动态:declare @s nvarchar(4000)set @s=''Select @s=@s+','+quotename([Course])+'=max(case when [Course]='+quotename([Course],'''')+' then [Score] else 0 end)'from Class group by[Course]exec('select [Student]'+@s+',[总成绩]=sum([Score]) from Class group by [Student]')--加多一列(学科平均分用avg([Score]))生成动态:select [Student], [数学]=max(case when [Course]='数学' then [Score] else 0 end), [物理]=max(case when [Course]='物理' then [Score] else 0 end), [英语]=max(case when [Course]='英语' then [Score] else 0 end), [语文]=max(case when [Course]='语文' then [Score] else 0 end), [总成绩]=sum([Score]) --加多一列(学科平均分用avg([Score]))from Class group by [Student]go--2005方法:动态:declare @s nvarchar(4000)Select @s=isnull(@s+',','')+quotename([Course]) from Class group by[Course] --isnull(@s+',','') 去掉字符串@s中第一个逗号exec('select [Student],'+@s+',[总成绩] from (select *,[总成绩]=sum([Score])over(partition by [Student]) from Class) a pivot (max([Score]) for [Course] in('+@s+'))b ')生成静态:select [Student],[数学],[物理],[英语],[语文],[总成绩] from (select *,[总成绩]=sum([Score])over(partition by [Student]) from Class) a --平均分时用avg([Score])pivot (max([Score]) for [Course] in([数学],[物理],[英语],[语文]))b 生成格式:/*Student 数学 物理 英语 语文 总成绩------- ----------- ----------- ----------- ----------- -----------李四 77 85 65 65 292张三 87 90 82 78 337(2 行受影响)*/go--2、列转行--> --> (Roy)生成測試數據 if not object_id('Class') is null drop table ClassGoCreate table Class([Student] nvarchar(2),[数学] int,[物理] int,[英语] int,[语文] int)Insert Classselect N'李四',77,85,65,65 union allselect N'张三',87,90,82,78Go--2000:动态:declare @s nvarchar(4000)select @s=isnull(@s+' union all ','')+'select [Student],[Course]='+quotename(Name,'''')--isnull(@s+' union all ','') 去掉字符串@s中第一个union all+',[Score]='+quotename(Name)+' from Class'from syscolumns where ID=object_id('Class') and Name not in('Student')--排除不转换的列order by Colidexec('select * from ('+@s+')t order by [Student],[Course]')--增加一个排序生成静态:select * from (select [Student],[Course]='数学',[Score]=[数学] from Class union all select [Student],[Course]='物理',[Score]=[物理] from Class union all select [Student],[Course]='英语',[Score]=[英语] from Class union all select [Student],[Course]='语文',[Score]=[语文] from Class)t order by [Student],[Course]go--2005:动态:declare @s nvarchar(4000)select @s=isnull(@s+',','')+quotename(Name)from syscolumns where ID=object_id('Class') and Name not in('Student') order by Colidexec('select Student,[Course],[Score] from Class unpivot ([Score] for [Course] in('+@s+'))b')goselect Student,[Course],[Score] from Class unpivot ([Score] for [Course] in([数学],[物理],[英语],[语文]))b生成格式:/*Student Course Score------- ------- -----------李四 数学 77李四 物理 85李四 英语 65李四 语文 65张三 数学 87张三 物理 90张三 英语 82张三 语文 78(8 行受影响)*/