sql - SQL Server - 是否可以在行更新之前返回现有的列值？

Question

我正在编写一个查询来更新用户对论坛帖子（ForumPosts ）的投票（ ForumVotes ）。用户可以投票赞成或反对（投票将等于 1 或 -1）。此问题专门针对更改用户的投票，因此ForumVotes表中已存在投票记录。

ForumPosts表存储每个帖子的总分，因此我需要保持该字段同步。要重新计算总分，我需要先减去旧票，然后再添加新票，因此我需要在更新用户投票记录之前获取旧票。

我知道我可以用 2 个查询来做到这一点，但我想知道是否有可能（在 SQL Server 2008 中）更新在执行更新之前返回列的值？

这是一个例子：

TABLE ForumPosts (
    postID bigint,
    score int,
    ... etc
)

-- existing vote is in this table:

TABLE ForumVotes (
    postFK bigint,
    userFK bigint,
    score int
)

更新用户投票的简单查询

UPDATE ForumVotes 
SET score = @newVote 
WHERE postFK = @postID
AND userFK = @userID

可以修改此查询以返回更新前的旧分数吗？

Answer 1

试试 OUTPUT 子句：

declare @previous table(newscore int, Oldscore int, postFK int, userFK int)

UPDATE ForumVotes 
SET score = @newVote 
OUTPUT inserted.score,deleted.score, deleted.postFK, deleted.userFK into @previous
WHERE postFK = @postID
AND userFK = @userID

select * from @previous

Answer 2

如果是single row affected query (ie; update using key(s))则；

declare @oldVote varchar(50)

update ForumVotes 
set score = @newVote, @oldVote = score 
where postFK = @postId and userFK = @userId

--to receive the old value
select @oldVote 

Answer 3

I'll expand upon @HLGEM's answer by showing you don't need an intermediate @previous table, you can rely on OUTPUT returning data directly without any variables, only aliasing:

UPDATE
    ForumVotes
SET
    Score = @newVote
OUTPUT
    INSERTED.Score AS NewScore,
    DELETED.Score  AS OldScore
WHERE
    PostFK = @postId AND
    USerFK = @userId

If you run this directly, you'll get a table returned with 1 row of data and 2 columns: NewScore and OldSCore.