如何合并2个sql语句并立刻获得结果

Question

我无法弄清楚如何合并这两个查询并一次得到结果。

 $q1 = "SELECT q.id, q.content, a.id, a.content, a.addDT, acr.score 
      FROM questions_and_exercises q, `lesson-question` lq 
      LEFT JOIN answers a ON (a.uid=? AND a.qid=lq.qid) 
      LEFT JOIN `answer_chk_results` acr ON (acr.aid=a.id) 
      WHERE q.id=lq.qid AND lq.lid=?"; 
     $q2 ="SELECT q.id, q.content, a.id, a.content, a.addDT, acr.score 
      FROM questions_and_exercises q, 
      `questions from-to` qft 
      LEFT JOIN answers a ON (a.uid=? AND a.qid=qft.qid) 
      LEFT JOIN `answer_chk_results` acr ON (acr.aid=a.id) 
      WHERE q.id=qft.qid AND qft.to_uid=?"; 

推荐？在此先感谢

Answer 1

使用UNION这个问题。

然而，在这种情况下，我不认为甚至需要一个UNION：

$q1 = "SELECT q.id, q.content, a.id, a.content, a.addDT, acr.score 
     FROM questions_and_exercises q, `lesson-question` lq 
     LEFT JOIN answers a 
     ON a.qid=lq.qid 
     LEFT JOIN `answer_chk_results` acr 
     ON acr.aid=a.id 
     WHERE q.id=lq.qid AND a.uid = ? (lq.lid = ? OR qtf.to_uid = a.uid)"; 

将这些结果2扣杀连成多行。

$q1 = "SELECT q.id, q.content, a.id, a.content, a.addDT, acr.score 
     FROM questions_and_exercises q, `lesson-question` lq 
     LEFT JOIN answers a ON (a.uid=? AND a.qid=lq.qid) 
     LEFT JOIN `answer_chk_results` acr ON (acr.aid=a.id) 
     WHERE q.id=lq.qid AND lq.lid=? 
     UNION # ALL 
     SELECT q.id, q.content, a.id, a.content, a.addDT, acr.score 
     FROM questions_and_exercises q, 
     `questions from-to` qft 
     LEFT JOIN answers a ON (a.uid=? AND a.qid=qft.qid) 
     LEFT JOIN `answer_chk_results` acr ON (acr.aid=a.id) 
     WHERE q.id=qft.qid AND qft.to_uid=?"; 

要么使用UNION或UNION ALL取决于您是否要合并相同的行或不上。 UNION要求两个SELECT具有相同数量的列，并将使用第一个SELECT的别名。

您可能宜生像这最后询问：

 SELECT q.id, q.content, a.id, a.content, a.addDT, acr.score 
     FROM questions_and_exercises q, 
     `questions from-to` qft 
     LEFT JOIN answers a 
     ON a.qid=qft.qid 
     LEFT JOIN `answer_chk_results` acr 
     ON acr.aid=a.id 
     WHERE q.id=qft.qid AND qft.to_uid=? AND qtf.to_uid = a.uid 

Basicly，因为它是相同的值，它足以与?比较to_uid，然后用uid比较to_uid。这与通过ON比较它们的结果是一样的。

Answer 2

使用UNION ALL

$q1 = "SELECT q.id, q.content, a.id, a.content, a.addDT, acr.score 
      FROM questions_and_exercises q, `lesson-question` lq 
      LEFT JOIN answers a ON (a.uid=? AND a.qid=lq.qid) 
      LEFT JOIN `answer_chk_results` acr ON (acr.aid=a.id) 
      WHERE q.id=lq.qid AND lq.lid=? union all 
      SELECT q.id, q.content, a.id, a.content, a.addDT, acr.score 
      FROM questions_and_exercises q, 
      `questions from-to` qft 
      LEFT JOIN answers a ON (a.uid=? AND a.qid=qft.qid) 
      LEFT JOIN `answer_chk_results` acr ON (acr.aid=a.id) 
      WHERE q.id=qft.qid AND qft.to_uid=?";