使用 SQL 合并或 UPDATE / INSERT

Question

我有一个表 (Customer_Master_File)，需要从转储到文件夹中的平面文件中进行更新。我有一个 SSIS 包，可以运行以获取平面文件并将它们导入临时表 (temp_Customer_Master_File)

我无法做到的是：

对于临时表中的每条记录，如果主表中存在Customer_Number，则更新它，如果不插入临时表的内容。

我正在更新记录的所有字段，而不是查找单个字段的更改。

我尝试了 SQL Merge 功能，但是当源数据中有多个记录时它会出错。

平面文件包含对客户记录的更改，一次可能有多个更改。我只想根据需要通过插入或更新来处理每条记录。

我还尝试执行 INSERT INTO MASTER_FILE FROM TEMP_TABLE WHERE CUSTOMER_NUMBER NOT IN MASTER_FILE，但这在遇到重复的源行时也会失败并出现 PK 错误。

Answer 1

UPDATE m SET 
  col2 = t.col2, 
  col3 = t.col3 -- etc. - all columns except Customer_Number
FROM dbo.Master_File AS m
INNER JOIN 
(
  SELECT 
    Customer_Number, rn = ROW_NUMBER() OVER
    (
      PARTITION BY Customer_Number ORDER BY [timestamp_column] DESC
    ), col2, col3, ... etc ...
  FROM dbo.Temp_Table
) AS t
ON m.Customer_Number = t.Customer_Number
WHERE t.rn = 1;

INSERT dbo.Master_File(Customer_Number, col2, col3, ...etc...)
  SELECT Customer_Number, col2, col3, ...etc...
  FROM 
  (
    SELECT 
      Customer_Number, rn = ROW_NUMBER() OVER 
      (
        PARTITION BY Customer_Number ORDER BY [timestamp_column DESC
      ),
      col2, col3, ...etc...
    FROM dbo.Temp_Table AS t 
    WHERE NOT EXISTS 
    (
      SELECT 1 FROM dbo.Master_File AS m
      WHERE m.Customer_Number = t.Customer_Number
    )
  ) AS x WHERE rn = 1;

这会处理源表中不存在于目标表中的多行。我对列名做了一个假设，您必须对其进行调整。

MERGE 可能很诱人，但有几个原因我会回避它：

1. 语法令人生畏且难以记忆...
2. you don't get any more concurrency than the above approach unless you intentionally add specific locking hints...
3. there are many unresolved bugs with MERGE 可能还有更多尚未被发现的东西......

I recently published a cautionary tip here as well 和 have collected some other opinions here。