sql兩張表關聯更新字段

記錄，推薦使用第三種，個人覺得比較好

--第一種寫法,之前一直用，沒有在意
    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
    

    --第二種寫法,發現第一種寫法有些不符合語法，這種比第一種好
    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 

    --第三種寫法，這種方法更加簡潔，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