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[英]“Triple Join”?? Can an INNER-JOIN have have an add'l query after 'WHERE' to exclude rows from a 3rd table?
[英]Get only 1 row from 3rd table with inner join
所以我要獲取 3 個表:
問題、答案和成員。
這工作得很好,但問題是,我只想得到每個問題的第一行answers
。 因此,如果一個問題有 50 個答案,我只想顯示其中一個的片段。 我查看了子查詢和左連接,但它似乎不起作用。 我怎樣才能做到這一點?
$queryGQ = "SELECT
questions.q_id,
questions.question,
questions.description,
questions.link,
questions.m_id AS qMID,
questions.timestamp,
questions.linktitle,
questions.answers,
questions.upvotes,
answers.a_id,
answers.q_id AS qQID,
answers.answer,
members.m_id AS mMID,
members.navn,
members.avidaname
FROM
questions
INNER JOIN
answers ON answers.q_id = questions.q_id
INNER JOIN
members ON questions.m_id = members.m_id
WHERE public = '1'
ORDER BY questions.timestamp DESC LIMIT $TheLimit";
if ($stmtGQ = $con->prepare($queryGQ)) {
/* execute statement */
$stmtGQ->execute();
/* bind result variables */
$stmtGQ->bind_result($q_id, $question, $description, $link, $qMID, $timestamp, $linktitle, $answers, $upvotes, $aAID, $qQID, $answer, $mMID, $navn, $avidaname);
/* fetch values */
while ($stmtGQ->fetch()) {
//MAGIC HAPPENS
}
}
如果您想保留獲得最多贊成票的答案,那么您可以向子查詢添加另一個連接,它會為每個問題找到最受歡迎的答案。 然后,使用它來過濾您的結果集,使每個問題只有一個答案。
SELECT
q.q_id,
q.question,
q.description,
q.link,
q.m_id AS qMID,
q.timestamp,
q.linktitle,
q.answers,
q.upvotes,
a.a_id,
a.q_id AS qQID,
a.answer,
m.m_id AS mMID,
m.navn,
m.avidaname
FROM questions q
INNER JOIN answers a
ON a.q_id = q.q_id
INNER JOIN
(
SELECT q_id, MAX(upvotes) AS max_upvotes
FROM answers
GROUP BY q_id
) a2
ON a.q_id = a2.q_id AND a.upvotes = a2.max_upvotes
INNER JOIN members m
ON q.m_id = m.m_id
WHERE
public = '1'
ORDER BY
q.timestamp DESC;
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