关于mysql：如何使用单个查询更新SQL而不是使用php循环？


How to update SQL with single query and not with php loop?

本问题已经有最佳答案，请猛点这里访问。

这些是我的表：

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tbl_answers =>
  aid    
  qid    
  answer    
  uid    
  dateposted    
  emailnotify
  namedisplay
  status
  isbestanswer


tbl_questions =>
  qid
  question
  detail
  mcid
  cid
  uid    
  answercount
  dateposted
  status
  showname
  emailnotify
  question_type_id

我试过这个：

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UPDATE tbl_questions
JOIN (
SELECT id, COUNT(*) AS n
FROM tbl_questions JOIN tbl_answers ON qid = tbl_questions.qid
WHERE answercount ="0"
GROUP BY id
) AS T USING (id)
SET num = n
WHERE n > 0

我想更新那些得到更多答案而不是计算在内的问题：
tbl_questions => answersercount

如何更新比计算的问题更多的行？ (没有php循环)

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UPDATE tbl_questions
  JOIN (
    SELECT tbl_questions.qid, COUNT(*) AS n
    FROM tbl_questions JOIN tbl_answers ON tbl_answers.qid = tbl_questions.qid  
    GROUP BY qid
  ) AS T USING (qid)
SET answercount = n
WHERE n > 0'