为什么我的左加入不起作用?

尽管你可以使用 left join ,请 not exists 似乎更清晰地实现了您的逻辑:

update P
    set Inactivity = p.Inactivity + 50,
        Processed = 1
    from dbo.Players  P
    where not exists (select
                      from dbo.PlayerToWar ptw
                      where ptw.PlayerID = p.PlayerId and ptw.WarID = @WarID
                     ) and
          p.Processed = 0;

这也修复了 = NULL 在您的查询中出现问题。

您必须使用is null而不是=null,我相信检查应该在x.playerid而不是p.playerid上进行。

UPDATE P
SET P.Inactivity = P.Inactivity + 50,
    P.Processed = 1
FROM dbo.Players as P
LEFT JOIN ( SELECT PlayerID
            FROM dbo.PlayerToWar
            WHERE WarID = @WarID
            ) X
ON P.PlayerID = X.PlayerID
WHERE X.PlayerID IS NULL and P.Processed = 0

UPDATE P
SET P.Inactivity = P.Inactivity + 50,
    P.Processed = 1
FROM dbo.Players as P
LEFT JOIN 
  dbo.PlayerToWar x      
ON P.PlayerID = x.PlayerID and x. WarID = @WarID   
WHERE x.PlayerID IS NULL and P.Processed = 0

个人偏好,但在我看来,最好不要将子查询放在括号内。原始查询永远不会命中任何结果,因为(可能)players表中的数据不允许空playerid。

where子句应具有x.playerid,该值为空。另外,p.processed=1应该在join语句中。

UPDATE P
SET P.Inactivity = P.Inactivity + 50,
    P.Processed = 1
FROM dbo.Players as P
LEFT JOIN ( SELECT PlayerID
            FROM dbo.PlayerToWar
            WHERE WarID = @WarID
            ) X
ON P.PlayerID = X.PlayerID
and P.Processed = 0
WHERE X.PlayerID is NULL