Question

我为自己加入一张桌子获得了一些很大的帮助，我正试图将它提升到一个新的水平。下面的SQL来自帮助，但我添加了以COUNT开头的选择行，到收件人表的内部联接以及分组依据。

SELECT
  Event.EventID              AS EventID,
  Event.EventDate            AS EventDateUTC,
  Participant2.ParticipantID AS AwayID,
  Participant1.ParticipantID AS HostID,
  COUNT(Recipient.ChallengeID) AS AllChallenges
FROM Event
  INNER JOIN Matchup Matchup1
    ON (Event.EventID = Matchup1.EventID)
  INNER JOIN Matchup Matchup2
    ON (Event.EventID = Matchup2.EventID)
  INNER JOIN Participant Participant1
    ON (Matchup1.Host = 1
        AND Matchup1.ParticipantID = Participant1.ParticipantID)
  INNER JOIN Participant Participant2
    ON (Matchup2.Host != 1
        AND Matchup2.ParticipantID = Participant2.ParticipantID)
  INNER JOIN Recipient
    ON (Event.EventID = Recipient.EventID)
WHERE Event.CategoryID = 1
    AND Event.Resolved = 0
    AND Event.Type = 1
GROUP BY Recipient.ChallengeID
ORDER BY EventDateUTC ASC

我的目标是计算收件人表中与Event中的EventID匹配的行数。这段代码工作正常除了，我还希望得到收件人中有0个匹配行的结果。我想要15行（=事件数），但我得到2行，一行计数为1，一行计数为2（适用于内部联接，因为样本收件人表中有3行，一行一个EventID，两个用于另一个EventID）。

我认为LEFT join或OUTER join是我正在寻找的，但我知道我不太了解表是如何实际连接的。 LEFT join在那里给了我一行0，恰好是EventID 1（表中的第一件事），但这就是全部。错误告诉我，我不能只将INNER连接更改为OUTER。我尝试了一些括号和一些子选择等，但似乎无法使它工作。

Answer 1

使用：

   SELECT e.eventid,
          e.eventdate AS EventDateUTC,
          p2.participantid AS AwayID,
          p1.participantid AS HostID,
          COUNT(r.challengeid) AS AllChallenges
     FROM EVENT e
     JOIN Matchup m1 ON m1.eventid = e.eventid
                    AND m1.host = 1
     JOIN Matchup m2 ON m2.eventid = e.eventid
                    AND m2.host != 1
     JOIN Participant p1 ON p1.participantid = m1.participantid
     JOIN Participant p2 ON p2.participantid = m2.participantid
LEFT JOIN RECIPIENT r ON r.eventid = e.eventid
    WHERE e.categoryid = 1
      AND e.resolved = 0
      AND e.type = 1
 GROUP BY e.eventid, e.eventdate, p2.participantid, p1.participantid
 ORDER BY e.eventdate

SQL Outer加入一堆Inner Joined结果

1 个答案: