一个常见Sql问题的解决
很多时候我们都需要实现如下的功能：
表TableM
结构如下：
数据如下：
表TableD
结构如下：
数据如下：
需要实现的功能如下：
具体的就不说了，大家仔细看了这几张图就知道实现什么了^-^
实现起来最直接方法就是用游标了，而且是嵌套游标，这个当然效率相当低了，不过随后会给出更好的实现方法^-^
这个方法需要建立一个临时表TableResult，它只有一个字段AllStr!!
SQL代码如下:
--方法一：嵌套游标
--表名 字段名
--TableD AStr BStr CStr
--TableM AStr BStr
--TableResult AllStr
--符合条件的数据放到表TheSameRecord
Select TableD.AStr,TableD.BStr,TableD.CStr
Into TheSameRecord
From TableM,TableD
Where TableM.AStr = TableD.AStr And TableM.BStr = TableD.BStr
Declare @AStr VarChar(50)
Declare @BStr VarChar(50)
Declare @CStr VarChar(50)
Declare @AllCStr VarChar(500)
Set @AllCStr = ''
Declare @iNext Bit
Set @iNext = 0
--外层游标
Declare Outer_Cursor Cursor For
Select Distinct AStr,BStr From TheSameRecord
Open Outer_Cursor
Fetch Next From Outer_Cursor Into @AStr, @BStr
While @@Fetch_Status = 0
Begin
--内层游标
Declare Inner_Cursor Cursor For
Select CStr From TheSameRecord Where AStr = @AStr And BStr = @BStr
Set @AllCStr = ''
Open Inner_Cursor
Fetch Next From Inner_Cursor Into @CStr
While @@Fetch_Status = 0
Begin
Set @AllCStr = @AllCStr + @CStr + ','
Fetch Next From Inner_Cursor Into @CStr
End
if (@iNext = 0)
Begin
Delete TableResult
Set @iNext = 1
End
Insert Into TableResult (AllStr) Values (SubString( @AllCStr,1, Len(@AllCStr)-1))
Print SubString( @AllCStr,1, Len(@AllCStr)-1 )
Close Inner_Cursor
DealLocate Inner_Cursor
Fetch Next From Outer_Cursor Into @AStr, @BStr
End
Close Outer_Cursor
DealLocate Outer_Cursor
--删除表TheSameRecord
Drop Table TheSameRecord
Select * From TableResult
结果如下:
但是马上又想到了另外一种方法实现，因为函数本身就可以对数据进行循环，那么如果用函数来实现的话，
一则效率高，
二则代码量少
那么就有如下实现了：
--方法二：函数
Create Function AddStr(@AStr VarChar(50), @BStr VarChar(50))
Returns VarChar(8000)
As
Begin
Declare @ALLStr Varchar(8000)
Set @ALLStr=''
Select @ALLStr = @ALLStr + ',' + Cast(CStr As VarChar) From TheSameRecord
Where AStr = @AStr And BStr = @BStr
Set @ALLStr = Right(@ALLStr,Len(@ALLStr)-1)
Return(@ALLStr)
End
Go
Select TableD.AStr,TableD.BStr,TableD.CStr
Into TheSameRecord
From TableM,TableD
Where TableM.AStr = TableD.AStr And TableM.BStr = TableD.BStr
Go
Select Distinct AStr,BStr,dbo.AddStr(AStr,BStr) As AllStr From TheSameRecord
Drop Table TheSameRecord
结果如下:
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