基於來自SQL服務器中另一個表的行值獲取特定的列和行數據

Question

有誰知道是否可以基於另一個表中的行值從表中的列中獲取數據？

例如

表1：

Name| Date 
----|----- 
Bob | D1 
Jon | D2 
Stu | D3 
Amy | D4 

表2：

Date |Bob |Jon |Stu |Amy 
-----|----|----|----|---- 
D1 | A | B | C | D 
D2 | B | C | D | A 
D3 | C | D | A | B 
D4 | D | A | B | C 

我需要匹配的日期，但通過正確的信帶給每個名稱

因此，表3是：

Name| Date | Letter 
----|------|------- 
Bob | D1 | A 
Jon | D2 | C 
Stu | D3 | A 
Amy | D4 | C 

歡迎任何建議。

謝謝

Answer 1

有很多方法可以實現所需的輸出。我的解決方案使用遊標和動態TSQL的組合。

下面是代碼，評論步步：

--1. create test tables 
create table table1 ([Name] nvarchar(50),[Date] nvarchar(50)) 
create table table2 ([Date] nvarchar(50),Bob nvarchar(50),Jon nvarchar(50),Stu nvarchar(50),Amy nvarchar(50)) 
create table table3 ([Name] nvarchar(50),[Date] nvarchar(50),[Letter] nvarchar(50)) 

--2. populate test tables 
insert into table1 
      select 'Bob','D1' 
union all select 'Jon','D2' 
union all select 'Stu','D3' 
union all select 'Amy','D4' 

insert into table2 
      select 'D1','A','B','C','D' 
union all select 'D2','B','C','D','A' 
union all select 'D3','C','D','A','B' 
union all select 'D4','D','A','B','C' 

--3. declare variables 
DECLARE @query  NVARCHAR(max); --this variable will hold the dynamic TSQL query 
DECLARE @name  NVARCHAR(50); 
DECLARE @date  NVARCHAR(50); 
DECLARE @result  NVARCHAR(50)  --this variable will hold "letter" value returned by dynamic TSQL query 
DECLARE @testCursor CURSOR; 

--4. define the cursor that will scan all rows in table1 
SET @testCursor = CURSOR FOR SELECT [Name], [Date] FROM table1; 

OPEN @testCursor; 
    FETCH NEXT FROM @testCursor INTO @name, @date; 
    WHILE @@FETCH_STATUS = 0 
     BEGIN 
      --5. for each row in table 1 create a dynamic query that retrieves the correct "Letter" value from table2 
      set @query = 'select @res=' + @name + ' from table2 where [Date] =''' + @date +'''' 

      --6. executes dynamic TSQL query saving result in @result variable 
      EXECUTE sp_executesql @query, N'@res nvarchar(50) OUTPUT', @res=@result OUTPUT 

      --inserts data in table3 that holds final results 
      insert into table3 select @name, @date, @result 

      FETCH NEXT FROM @testCursor INTO @name, @date; 
     END 
CLOSE @testCursor; 
DEALLOCATE @testCursor; 

select * from table1 
select * from table2 
select * from table3 

下面是結果。前兩個表顯示輸入，第三個表包含實際的結果：

Answer 2

如果你是無柱會有限制在尋找方法，你可以試試這個。 讓您的餐桌名稱爲@ table1，@ table2。然後：

select 
    [Name]  = [t1].[Name] 
    ,[Date]  = [t1].[Date] 
    ,[Letter] = [col2].[value]('.', 'varchar(10)')  
from 
    @table1 as [t1] 
cross apply 
    (
     select [t2_xml] = cast((select * from @table2 for xml path('t2')) as xml) 
    ) as [t2] 
cross apply 
    [t2].[t2_xml].[nodes]('t2[Date/text()=sql:column("[t1].[Date]")]') as [tab]([col]) 
cross apply 
    [col].[nodes]('*[local-name(.)=sql:column("[t1].[Name]")]') as [tab2]([col2]);