这个问题是关于 Doctrine 和 Symfony2 的。我使用 Doctrine DQL 进行了查询。Doctrine 会生成这样的 SQL；
SELECT f0_.id AS id0, f0_.nom AS nom1, f0_.prenom AS prenom2, f0_.email AS email3, p1_.move_distance AS move_distance4, a2_.adresse1 AS adresse15, a2_.adresse2 AS adresse26, p3_.nom AS nom7, v4_.nom AS nom8, v4_.url AS url9, v4_.cp AS cp10, v4_.insee AS insee11, v4_.lat AS lat12, v4_.lng AS lng13, COUNT(f0_.id) AS sclr17
FROM person_teacher p1_
INNER JOIN fos_user f0_ ON p1_.id = f0_.id
LEFT JOIN person_lesson p7_ ON f0_.id = p7_.person_id
LEFT JOIN lesson l6_ ON l6_.id = p7_.lesson_id AND (l6_.id = 1)
LEFT JOIN person_teacher_language p9_ ON p1_.id = p9_.personteacher_id
LEFT JOIN language l8_ ON l8_.id = p9_.language_id AND (l8_.id = 1)
LEFT JOIN note_value n10_ ON p1_.id = n10_.personTeacher_id
LEFT JOIN pays p3_ ON f0_.id_pays = p3_.id
LEFT JOIN note n5_ ON n10_.id_note = n5_.id
LEFT JOIN person_teacher_adresse p11_ ON p1_.id = p11_.personteacher_id
LEFT JOIN adresse a2_ ON a2_.id = p11_.adresse_id
LEFT JOIN ville v4_ ON a2_.id_ville = v4_.id
GROUP BY f0_.id LIMIT 2147483647 OFFSET 0;
问题在于这些连接：
LEFT JOIN person_lesson p7_ ON f0_.id = p7_.person_id
LEFT JOIN lesson l6_ ON l6_.id = p7_.lesson_id AND (l6_.id = 1)
LEFT JOIN person_teacher_language p9_ ON p1_.id = p9_.personteacher_id
LEFT JOIN language l8_ ON l8_.id = p9_.language_id AND (l8_.id = 1)
如果我删除它们，请求就会起作用。长请求，但有效。通过连接，请求是无限的（MySQL 在 500 万之后使用了 99.9% 的 CPU 时间）或者可能非常长，但无论如何，太长了。
如何优化这个查询？
（PS：我认为AND (l6_.id = 1)andAND (l8_.id = 1)会充当“过滤器”并立即删除不必要的行，但是不，这会使事情变得更糟：如果我删除这些条件并where在最后添加子句会更快，例如WHERE (l6_.id = 1) AND (l8_.id = 1)：）
这是我的 DQL 代码：
$retour = $this->createQueryBuilder('p')
->select(array(
'p.id',
'p.nom',
'p.prenom',
'p.email',
'p.moveDistance',
'a.adresse1',
'a.adresse2',
'pn.nom as pays',
'v.nom AS ville_nom',
'v.url',
'v.cp',
'v.insee',
'v.lat',
'v.lng',
'ROUND(' .
$mul.' * ' .
'ACOS( ' .
'COS( RADIANS( '.$lat.')) * '.
'COS( RADIANS( v.lat )) * '.
'COS( RADIANS( v.lng )-radians('.$lng.')) + '.
'SIN( RADIANS( '.$lat.' )) * '.
'SIN( RADIANS( v.lat )) ' .
')'.
',2) AS distance',
($in_kilometers?'\'km\'':'\'miles\'').' AS unit',
'ROUND( AVG(n.importance), 1) AS importance',
'COUNT(p.id) AS total'
))
->leftJoin('p.noteValues', 'nv')
->leftJoin('p.paysNaissance', 'pn')
->leftJoin('nv.note', 'n')
->leftJoin('p.adresses', 'a')
->leftJoin('a.ville', 'v');
/* (!) Optimizer: find out why if I do a join "ON"
* it endlessly query. I did classical "join" then a "WHERE"
* at the end. Find out why this method is faster:
*/
if ($lesson_id>0) {
$retour = $retour
->leftJoin('p.lessons', 'le');
}
if ($language_id>0) {
$retour = $retour
->leftJoin('p.languages', 'ln');
}
if (($lesson_id>0) && ($language_id>0)) {
$retour = $retour
->where('le.id = :lesson_id')
->andWhere('ln.id = :language_id');
}
elseif ($lesson_id>0) {
$retour = $retour
->where('le.id = :lesson_id');
}
elseif ($language_id>0) {
$retour = $retour
->where('ln.id = :language_id');
}
$retour = $retour
->groupBy('p.id')
->having('distance>:dmin')
->andHaving('distance<=:dmax')
->addOrderBy($order_by_1, $order_sens_1)
->addOrderBy($order_by_2, $order_sens_2);
$params=array(
'dmin' => $distance_min,
'dmax' => $distance_max
);
if ($lesson_id>0) {
$params['lesson_id']= $lesson_id;
}
if ($language_id>0) {
$params['language_id']= $language_id;
}
$retour = $retour->setParameters($params);
$retour = $retour
->setFirstResult( $offset )
->setMaxResults( $limit );
return $retour;