使用在 sql server 中具有多行的另一个表更新主表行

Question

我有 2 个具有公共列 ID 的表

Table A:
ID   value1    value2    value3
------------------------------------        
 1     0         0        0

Table B:
ID    value_type      value   
--------------------------------------          
1     value1          0.01  
2     value2          0.02
3     value3          0.03

我想使用表 b 的值更新表 A 的值，

Final Output :

ID   value1    value2    value3
-----------------------------------------
1     0.01       0.02      0.03

谁能告诉我如何编写查询并获取上述结果，非常感谢！我试过加入，支点。一切都没有结果。

Answer 1

一种快速（但不可扩展）的解决方案是使用更新语句，通过条件聚合连接到派生表：

UPDATE T
SET value1 = v1,
    value2 = v2,
    value3 = v3
FROM TableA T
JOIN 
(
    SELECT 1 As ID
           MAX(CASE WHEN value_type = 'value1' THEN value END) As v1,
           MAX(CASE WHEN value_type = 'value2' THEN value END) As v2,
           MAX(CASE WHEN value_type = 'value3' THEN value END) As v3
    FROM TableB
) V
    ON T.ID = V.ID

Answer 2

使用 pivot 我们可以做到这一点

因为我将数据存储到一个表中，然后我才进行更新

DECLARE @cols AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX);

SET @cols = STUFF((SELECT distinct ',' + QUOTENAME(c.value_type)
            FROM #b c
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @query = 'SELECT rn as id , '  + (@cols) + ' into dynamictable  from 
            (
                select *,ROW_NUMBER() OVER(PARTITION BY ID ORDER BY ID ) AS RN
                from #b
           ) x
            pivot 
            (
                MAX(VALUEE)
                for VALUE_TYPE in (' + @cols + ')
            ) p 
          '


exec(@query)
UPDATE T
SET T.value1 = V.value1,
    T.value2 = V.value2,
    T.value3 = V.value3
FROM #a T
JOIN 
(SELECT   id ,MAX(VALUE1)VALUE1 , MAX(VALUE2)VALUE2, MAX(VALUE3)VALUE3 
FROM  dynamictable
GROUP BY id
) V
    ON T.ID = V.ID