Question

我无法弄清楚如何合并这两个查询并立即获得结果。

        $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=?";

Suggetions？提前致谢

Answer 1

就此问题使用UNION。

但是在这种情况下，我认为甚至不需要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)";

它会将这两个结果粉碎成更多行。

$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=?";

使用UNION或UNION ALL，具体取决于您是否要合并相同的行。 UNION要求两个SELECT具有相同数量的列，并且将使用第一个SELECT个别名。

你可以放宽上次查询，如下所示：

        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

基本上，因为它是相同的值，所以将to_uid与?进行比较就足够了，然后将to_uid与uid进行比较。与通过ON比较它们的结果相同。

Answer 2

使用全部联盟

$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=?";

如何合并2个sql语句并立即获得结果

2 个答案: