更新语句中的多个案例

Question

我有两个旧程序来更新用户数据，一个使用MERGE语句，另一个使用简单的UPDATE语句。 在这两种情况下，我都必须编写一个逻辑来更新地址、城市、state 和 zip。 如果地址是新地址，请在PreviousAddress字段中更新旧地址，并在Address字段中输入新地址。

为了简单起见，我已经淡化了这个问题。

create table t1 (id int, address varchar(25), city varchar(25), state varchar(25), zip varchar(25), paddress varchar(25), pcity varchar(25), pstate varchar(25), pzip varchar(25))

insert into t1 values (1, '1 roger st', 'edison', 'nj', '98211', null, null, null, null)

declare @address varchar(25) = '6 roger st'
declare @city varchar(25) = 'edison'
declare @state varchar(25) = 'nj'
declare @zip  varchar(25) = '98191'
declare @paddress varchar(25) = null
declare @pcity varchar(25) = null
declare @pstate varchar(25) = null
declare @pzip  varchar(25) = null

update t1 
  set address = @address, city=@city, state=@state, zip=@zip,
  paddress = COALESCE(CASE when Address <> @address THEN Address ELSE @pAddress END, PAddress),
  pcity = COALESCE(CASE when city <> @city THEN city ELSE @pcity END, pcity),
  pstate = COALESCE(CASE when [state] <> @state THEN state ELSE @pstate END, pstate),
  pzip = COALESCE(CASE when zip <> @zip THEN zip ELSE @pzip END, pzip)

select * from t1

我以为我已经解决了这个问题，但结果不是我们想要的，如果地址字段不同，则解决方案有效。 但是，如果很少有地址字段没有改变，那么解决方案就会失败。 我想确定是否any地址字段发生变化，我需要用新的地址字段更新所有以前的地址字段。 在上面的例子中，只有地址和 zip 改变了，城市和 state 没有改变。 City 和 State 未更新并显示null 。

我们如何解决UPDATE语句和MERGE语句的问题？

这是我的合并声明：

MERGE dbo.User AS TARGET
    USING
    (
        SELECT @USERID as USERID,
        @USERNAME as USERNAME,
        @ADDRESS as ADDRESS,
        @City as CITY,
        @State as STATE,
        @ZIP as ZIP,
        @PREVIOUSADDRESS as PREVIOUSADDRESS,
        @PREVIOUSCity as PREVIOUSCITY,
        @PREVIOUSSTATE as PREVIOUSSTATE,
        @PREVIOUSZIP as PREVIOUSZIP
    ) as SOURCE
    (
        USERID,
        USERNAME,
        ADDRESS,
        CITY,
        STATE,
        ZIP,
        PREVIOUSADDRESS,
        PREVIOUSCITY,
        PREVIOUSSTATE,
        PREVIOUSZIP
    ) ON (TARGET.USERID = SOURCE.USERID)
    WHEN NOT MATCHED THEN
        INSERT ( USERID,
           USERNAME,
           ADDRESS,
           CITY,
           STATE,
           ZIP,
           PREVIOUSADDRESS,
           PREVIOUSCITY,
           PREVIOUSSTATE,
           PREVIOUSZIP )
        VALUES ( SOURCE.USERID,
           SOURCE.USERNAME,
           SOURCE.ADDRESS,
           SOURCE.CITY,
           SOURCE.STATE,
           SOURCE.ZIP,
           SOURCE.PREVIOUSADDRESS,
           SOURCE.PREVIOUSCITY,
           SOURCE.PREVIOUSSTATE,
           SOURCE.PREVIOUSZIP


)
        WHEN MATCHED 
            UPDATE
               SET USERNAME = SOURCE.USERNAME,
                   ADDRESS = SOURCE.ADDRESS,
                   ADDRESS = SOURCE.CITY,
                   ADDRESS = SOURCE.STATE,
                   ADDRESS = SOURCE.ZIP,
                   PREVIOUSADDRESS = (CASE WHEN  TARGET.ADDRESS <> SOURCE.ADDRESS THEN TARGET.ADDRESS
                   ELSE SOURCE.PREVIOUSADDRESS END),
                   PREVIOUSCITY = (CASE WHEN  TARGET.CITY <> SOURCE.CITY THEN TARGET.CITY
                   ELSE SOURCE.CITY END),
                   PREVIOUSSTATE = (CASE WHEN  TARGET.STATE <> SOURCE.STATE THEN TARGET.STATE
                   ELSE SOURCE.STATE END),
                   PREVIOUSZIP = (CASE WHEN  TARGET.ZIP <> SOURCE.ZIPTHEN TARGET.ZIP
                   ELSE SOURCE.PREVIOUSZIP END)