sql两张表关联更新字段

记录，推荐使用第三种，个人觉得比较好

--第一种写法,之前一直用，没有在意
    UPDATE sr_t_TCodeUserReciveCfg SET fUserID=a.fUserID,fImportFlag=NULL FROM dbo.vw_userinfo AS a INNER JOIN dbo.sr_t_TCodeUserReciveCfg AS b ON a.sLoginName=b.fImportFlag
    WHERE b.fImportFlag IS NOT NULL

    --第二种写法,发现第一种写法有些不符合语法，这种比第一种好
    UPDATE b SET fUserID=a.fUserID,fImportFlag=NULL FROM dbo.vw_userinfo AS a INNER JOIN dbo.sr_t_TCodeUserReciveCfg AS b ON a.sLoginName=b.fImportFlag
    WHERE b.fImportFlag IS NOT NULL 

    --第三种写法，这种方法更加简洁，是不是？？？
    UPDATE sr_t_TCodeUserReciveCfg SET fUserID=a.fUserID,fImportFlag=NULL FROM vw_userinfo a WHERE fImportFlag=a.sLoginName AND fImportFlag IS NOT NULL