oracle查询检查不存在于其他表中

Question

我有以下查询：

select vw.CONFERENCEID, alert.ALERTID, del.CHANNELID, del.DOCUMENTTEMPLATEID,
       vw.starttime, vw.CONFERENCEID, alert.ALERTATTRIBUTEID,
       alert.ALERTCATEGORYID, alert.ATTACHMENT, alert.ATTACHMENTLOCATION,
       alert.ATTACHMENTNAME
  from TBLMCONFERENCE vw,
       TBLMSYSTEMALERTS alert,
       TBLMALERTDELIVERYREL del,
       tblmstandardmaster sm 
 WHERE alert.Alertid = del.alertid
   and sm.masterid = del.CHANNELID
   and alert.SYSTEMGENERATED = 'N'
   and alert.alertid not in (
       select sent.ALERTID
         from TBLMSENTALERTHISTORY sent
        where sent.REFACCOUNTID = vw.conferenceid
          and sent.ALERTID = alert.ALERTID
          and sent.CHANNELID = del.CHANNELID
          and sent.RESETFLAG = 'N')

即使TBLMSENTALERTHISTORY表中存在匹配记录，我也会收到记录。

此查询有什么问题吗？

Answer 1

我不确定你为什么要获取数据，也许你可以用一些表和插入来构建一个小例子。

但是，我可以指出您对NOT IN运算符的使用不是标准的：在大多数情况下，您不应该使用IN和NOT IN运算符将子查询加入主查询（这是多余的）。相反，你会写：

SELECT *
  FROM TBLMCONFERENCE vw,
       TBLMSYSTEMALERTS alert,
       TBLMALERTDELIVERYREL del,
       tblmstandardmaster sm
 WHERE alert.Alertid = del.alertid
   AND sm.masterid = del.CHANNELID
   AND alert.SYSTEMGENERATED = 'N'
   AND (alert.alertid, del.CHANNELID, vw.conferenceid)
       NOT IN (SELECT sent.ALERTID, sent.CHANNELID, sent.conferenceid
                 FROM TBLMSENTALERTHISTORY sent
                WHERE sent.RESETFLAG = 'N')

在您的情况下，您可以直接使用子查询NOT EXISTS：

SELECT *
  FROM TBLMCONFERENCE vw,
       TBLMSYSTEMALERTS alert,
       TBLMALERTDELIVERYREL del,
       tblmstandardmaster sm
 WHERE alert.Alertid = del.alertid
   AND sm.masterid = del.CHANNELID
   AND alert.SYSTEMGENERATED = 'N'
   AND NOT EXISTS
          (SELECT sent.ALERTID
             FROM TBLMSENTALERTHISTORY sent
            WHERE sent.REFACCOUNTID = vw.conferenceid
              AND sent.ALERTID = alert.ALERTID
              AND sent.CHANNELID = del.CHANNELID
              AND sent.RESETFLAG = 'N')

请注意，通常NOT IN和NOT EXISTS不相同，because of NULLs。