求一个SQL,最好不用反复查询

[从不签到]

A表
ItemID ID1, ID2, ID3, ID4, F1,F2,F3
A001 kg kg m kg

B表
ItemID From To Factor
A001 kg kg 1
A001 m kg 2

现在想求得是，a表的ID1->ID4, ID2->ID4, ID3->ID4 之间的转换

结果就是
ItemID ID1, ID2, ID3, ID4, F1,F2,F3
A001 kg kg m kg 1 1 2

[jamesrggg]

Declare @TmpDataA Table(
	ItemID NVarchar(100),
	ID1 Nvarchar(5),
	ID2 Nvarchar(5),
	ID3 Nvarchar(5),
	ID4 Nvarchar(5))

Insert Into @TmpDataA
Select 'A001','kg','kg','m','kg'

Declare @TmpDataB Table(
	ItemID NVarchar(100),
	FromS Nvarchar(5),
	ToS NVarchar(5),
	Factor Int)
Insert Into @TmpDataB
Select 'A001','kg','kg',1
Union
Select 'A001','m','kg',2

Select A.ItemID,A.ID1,A.ID2,A.ID3,A.ID4,Sum(F1) As F1,Sum(F2) As F2,Sum(F3) AsF3 From (
Select A.*,B.Factor As F1,0 As F2,0 As F3
	From @TmpDataA A
	Inner Join @TmpDataB B On B.ItemID = A.ItemID And B.FromS = A.ID1 And B.ToS = A.ID4
Union All
Select A.*,0 As F1,B.Factor As F2,0 As F3
	From @TmpDataA A
	Inner Join @TmpDataB B On B.ItemID = A.ItemID And B.FromS = A.ID2 And B.ToS = A.ID4
Union All
Select A.*,0 As F1,0 As F2,B.Factor As F3
	From @TmpDataA A
	Inner Join @TmpDataB B On B.ItemID = A.ItemID And B.FromS = A.ID3 And B.ToS = A.ID4) A
	Group By A.ItemID,A.ID1,A.ID2,A.ID3,A.ID4

[还在加载中灬]

--查询方式
SELECT A.ItemID,A.ID1,A.ID2,A.ID3,A.ID4
	,T1.Factor F1,T2.Factor F2,T3.Factor F3
FROM A
	LEFT JOIN B T1 ON A.ItemID=T1.ItemID AND A.ID1=T1.[From] AND A.ID4=T1.[To]
	LEFT JOIN B T2 ON A.ItemID=T2.ItemID AND A.ID2=T2.[From] AND A.ID4=T2.[To]
	LEFT JOIN B T3 ON A.ItemID=T3.ItemID AND A.ID3=T3.[From] AND A.ID4=T3.[To]

--更新方式
UPDATE A
SET F1=T1.Factor,F2=T2.Factor,F3=T3.Factor
FROM A
	LEFT JOIN B T1 ON A.ItemID=T1.ItemID AND A.ID1=T1.[From] AND A.ID4=T1.[To]
	LEFT JOIN B T2 ON A.ItemID=T2.ItemID AND A.ID2=T2.[From] AND A.ID4=T2.[To]
	LEFT JOIN B T3 ON A.ItemID=T3.ItemID AND A.ID3=T3.[From] AND A.ID4=T3.[To]

[从不签到]

--查询方式

SELECT A.ItemID,A.ID1,A.ID2,A.ID3,A.ID4
    ,T1.Factor F1,T2.Factor F2,T3.Factor F3
FROM A
    LEFT JOIN B T1 ON A.ItemID=T1.ItemID AND A.ID1=T1.[From] AND A.ID4=T1.[To]
    LEFT JOIN B T2 ON A.ItemID=T2.ItemID AND A.ID2=T2.[From] AND A.ID4=T2.[To]
    LEFT JOIN B T3 ON A.ItemID=T3.ItemID AND A.ID3=T3.[From] AND A.ID4=T3.[To]

这种方式的话，对B表是检索一次还是多次呢， 如果B表数据量很大，就会很慢吧

[jamesrggg]

引用 3 楼 hao1geren 的回复:

--查询方式

SELECT A.ItemID,A.ID1,A.ID2,A.ID3,A.ID4
    ,T1.Factor F1,T2.Factor F2,T3.Factor F3
FROM A
    LEFT JOIN B T1 ON A.ItemID=T1.ItemID AND A.ID1=T1.[From] AND A.ID4=T1.[To]
    LEFT JOIN B T2 ON A.ItemID=T2.ItemID AND A.ID2=T2.[From] AND A.ID4=T2.[To]
    LEFT JOIN B T3 ON A.ItemID=T3.ItemID AND A.ID3=T3.[From] AND A.ID4=T3.[To]

这种方式的话，对B表是检索一次还是多次呢， 如果B表数据量很大，就会很慢吧

三次,数据量不是超大的情况,应该分辨不出速度的变化