加入SQL表？

Question

我有这些表格。

Answer 1

这是10的入门者（我假设user_id列包含用户名，但实际上可能还有另一个表）：

SELECT q.question AS "Question",
       q.date_add AS "date",
       q.publish AS "publish",
       q.user_id AS "user name",
       c.name AS "category",
       a.answer AS "answer",
       a.publish AS "publish"
  FROM #__qa_question q
  LEFT OUTER JOIN #__qa_category_xref cx ON (cx.qid = q.qid)
  LEFT OUTER JOIN #__qa_category c ON (c.catid = cx.catid)
  LEFT OUTER JOIN #__qa_answer_xref ax ON (ax.qid = q.qid)
  LEFT OUTER JOIN #__qa_answer a ON (a.aid = ax.aid)

使用外部联接可确保即使没有答案或没有类别，您也会看到每个问题。

当然，如果（如外部参照表所示）每个问题有很多答案和许多类别，那么每个问题都会看到很多行，每个答案和类别组合都有一行。

Answer 2

假设#__ qa_category_xref.id是FK到#__qa_answer。 （假设没有#__qa_answer_xref表。）

select q.qid as [s/n], question, q.date_modify as [date], q.publish as publish
, user_id /*as no user table specified*/, c.name as category, answer, a.publish
from #__qa_question as q
join #__qa_category_xref as xref on q.qid = xref.qid
join #__qa_answer as a on a.aid = xref.id
join #__qa_category as c on c.catid = xref.catid

Answer 3

---

选择
q。问题，问题，
q.date_add作为日期，
q.publish as publish，
q.user_id为用户，
qcat.name作为类别，
qans.answer作为答案，
qans.publish as anspublish
来自  #__qa_question为q，
 #__qa_category_xref为qcatref，
 #__qa_category为qcat，
 #__qa_answer_xref为qansref
 #__qa_answer为qans
其中
q.qid = qcatref.qid
和qcat.catid = qcatref.catid
和q.quid = qansref.qid
和qans.aid = qansref.aid

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