Question

有一张表，其中多个列的值需要更正。然后有一个表，其中包含所有需要更正的值。

有没有简单的方法在MERGE语句中使用CROSS APPLY？

以我目前的知识，我需要为column1，column2等运行以下代码。

MERGE INTO target_table AS t
USING source_table AS s
ON t.key_column = s.key_column
    AND 'column_1' = s.correction_column
WHEN MATCHED THEN  
UPDATE SET t.column_1 = s.correction_value;

编辑：这些是目标，来源和预期结果的示例。

目标：

##    |  uid | col_1 | col_2 | col_3 | col_4 | col_5
----------------------------------------------------
## 1  |    1 |     a |     a |     a |     a |     a
## 2  |    2 |     a |     a |     a |     a |     a
## 3  |    3 |     a |     a |     a |     a |     a
## 4  |    4 |     a |     a |     a |     a |     a
## 5  |    5 |     a |     a |     a |     a |     a
## 6  |    6 |     a |     a |     a |     a |     a

来源：

##    |  uid |   col | value
----------------------------
## 1  |    1 | col_1 |     B
## 2  |    1 | col_2 |     C
## 3  |    4 | col_3 |     D
## 4  |    4 | col_4 |     E
## 5  |    5 | col_3 |     F

预期结果：

##    |  uid | col_1 | col_2 | col_3 | col_4 | col_5
----------------------------------------------------
## 1  |    1 |     B |     C |     a |     a |     a
## 2  |    2 |     a |     a |     a |     a |     a
## 3  |    3 |     a |     a |     a |     a |     a
## 4  |    4 |     a |     a |     D |     E |     a
## 5  |    5 |     a |     a |     F |     a |     a
## 6  |    6 |     a |     a |     a |     a |     a

Answer 1

您可以在括号中添加查询以创建派生表

示例

MERGE INTO target_table AS t
USING (select * from source_table a cross apply (select top 1 * from other_table b where b.id = a.id order by some_date desc) b2) AS s
ON t.key_column = s.key_column
    AND 'column_1' = s.correction_column
WHEN MATCHED THEN  
UPDATE SET t.column_1 = s.correction_value;

交叉申请合并

1 个答案: