具有多个更新的 SQLServer MERGE 语句

Question

我在尝试更新的SQL Server中有一个旧版存储过程。 这是一个很大的过程，但为了说明我的担忧，我会简化它。

过程是更新User表中的用户。 如果是新用户，他们INSERT ，否则UPDATE数据。 目前，他们使用MERGE语句来完成此操作。 我必须修改程序来处理PreviousAddress逻辑。 程序需要检查，如果用户是现有用户，并且传入程序的地址是新地址，那么我们需要将旧地址放在PreviousAddress字段中，新地址放在Address字段中。

这是当前的MERGE语句：

MERGE dbo.User AS TARGET
USING
(
    SELECT @USERID as USERID,
    @USERNAME as USERNAME,
    @ADDRESS as ADDRESS,
    @PREVIOUSADDRESS as PREVIOUSADDRESS
) as SOURCE
(
    USERID,
    USERNAME,
    ADDRESS,
    PREVIOUSADDRESS
) ON (TARGET.USERID = SOURCE.USERID)
WHEN NOT MATCHED THEN
    INSERT ( USERID,
       USERNAME,
       ADDRESS,
       PREVIOUSADDRESS )
    VALUES ( SOURCE.USERID,
       SOURCE.USERNAME,
       SOURCE.ADDRESS,
       SOURCE.PREVIOUSADDRESS )
WHEN MATCHED THEN
    UPDATE
       SET USERNAME = SOURCE.USERNAME,
           ADDRESS = SOURCE.ADDRESS,
           PREVIOUSADDRESS = SOURCE.PREVIOUSADDRESS

我想做这样的事情，当然两个MERGE语句是不可能的，但想知道如何实现类似的解决方案：

MERGE dbo.User AS TARGET
    USING
    (
        SELECT @USERID as USERID,
        @USERNAME as USERNAME,
        @ADDRESS as ADDRESS,
        @PREVIOUSADDRESS as PREVIOUSADDRESS
    ) as SOURCE
    (
        USERID,
        USERNAME,
        ADDRESS,
        PREVIOUSADDRESS
    ) ON (TARGET.USERID = SOURCE.USERID)
    WHEN NOT MATCHED THEN
        INSERT ( USERID,
           USERNAME,
           ADDRESS,
           PREVIOUSADDRESS )
        VALUES ( SOURCE.USERID,
           SOURCE.USERNAME,
           SOURCE.ADDRESS,
           SOURCE.PREVIOUSADDRESS )
    WHEN MATCHED AND TARGET.ADDRESS <> SOURCE.ADDRESS THEN
        UPDATE
           SET USERNAME = SOURCE.USERNAME,
               ADDRESS = SOURCE.ADDRESS,
               PREVIOUSADDRESS = TARGET.ADDRESS
    WHEN MATCHED AND TARGET.ADDRESS = SOURCE.ADDRESS THEN
        UPDATE
           SET USERNAME = SOURCE.USERNAME,
               ADDRESS = SOURCE.ADDRESS,
               PREVIOUSADDRESS = SOURCE.PREVIOUSADDRESS

我目前的解决方案是：在程序开始时，我 go 并从现有用户的USER表中获取当前地址，如果地址不匹配，则将现有地址存储在 memory 中。 然后我最后使用这个存储的地址进行比较和更新（在执行MERGE语句之后）。 像这样的东西：

IF @USERID IS NULL AND @ADDRESS IS NOT NULL 
BEGIN
  SELECT @CURRENTADDRESS = ADDRESS FROM USER WHERE USERID = @USERID AND ADDRESS <> @ADDRESS
END

<<ORIGINAL MERGE STATEMENT>>

IF @CURRENTADDRESS IS NOT NULL
BEGIN
  UPDATE USER SET PREVIOUSADDRESS = @CURRENTADDRESS WHERE USERID = @USERID
END

任何想法如何仅使用MERGE语句来解决此问题？

Answer 1

您可以使用 CASE WHEN 子句

MERGE dbo.User AS TARGET
    USING
    (
        SELECT @USERID as USERID,
        @USERNAME as USERNAME,
        @ADDRESS as ADDRESS,
        @PREVIOUSADDRESS as PREVIOUSADDRESS
    ) as SOURCE
    (
        USERID,
        USERNAME,
        ADDRESS,
        PREVIOUSADDRESS
    ) ON (TARGET.USERID = SOURCE.USERID)
    WHEN NOT MATCHED THEN
        INSERT ( USERID,
           USERNAME,
           ADDRESS,
           PREVIOUSADDRESS )
        VALUES ( SOURCE.USERID,
           SOURCE.USERNAME,
           SOURCE.ADDRESS,
           SOURCE.PREVIOUSADDRESS )
    WHEN MATCHED 
        UPDATE
           SET USERNAME = SOURCE.USERNAME,
               ADDRESS = SOURCE.ADDRESS,
               PREVIOUSADDRESS = (CASE WHEN  TARGET.ADDRESS <> SOURCE.ADDRESS THEN TARGET.ADDRESS
               ELSE SOURCE.PREVIOUSADDRESS END)