mysql关系慢

Question

<?php
$db = new mysqli(//editted out db credentials);

if($db->connect_errno > 0){
    die('Unable to connect to database [' . $db->connect_error . ']');
}
$sql = "SELECT m.ID, m.Title, GROUP_CONCAT(a.Title) AS Artist
FROM mp3s m
LEFT JOIN artist_relations ar ON ar.mp3ID = m.ID
LEFT JOIN artists a ON a.ID = ar.artistID
GROUP BY m.ID
ORDER BY ID
LIMIT 0,30;
";

if($result = $db->query($sql)){
echo "<table>";
while($row = $result->fetch_assoc()){
    echo "<tr>";  
    echo "<td>".$row['Title']."</td>";
    echo "<td>".$row['Artist']."</td>";
    echo "</tr>";  
}
echo "</table>";
}

?> 

这个查询工作正常，但速度很慢。

此数据库有3个字段：

`artists` : ID , Title
`mp3s` : ID , Title
`artist_relations` : mp3ID , artistID

我需要这个：

row1: titlemusic1 - artist1 , artist4 , artist5
row2: titlemusic2 - artist1
row3: titlemusic1 - artist3 , artist8
row4: titlemusic1 - artist9 , artist10
...

MP3、artist和artist_relations每个都有超过20000张唱片

EXPLAIN SELECT m.ID, m.Title, .... :
    id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra   
    1   SIMPLE  m   ALL     NULL    NULL    NULL    NULL    23718   Using temporary; Using filesort
    1   SIMPLE  ar  ALL     NULL    NULL    NULL    NULL    24337   
    1   SIMPLE  a   eq_ref  PRIMARY     PRIMARY     4   ganools_rj.ar.artistID  1   

--

如果不存在则创建表artist_relations(artistidint(11)NOT NULL，mp3idint(11)NOT NULL)engine=innoDB默认charset=latin1；

--

如果不存在则创建表artists(idint(11)不为NULL AUTO_INCREMENT，titlevarchar(155)不为NULL主键(id)))engine=innoDB DEFAULT charset=latin1 AUTO_INCREMENT=9005；

--

如果不存在mp3s(idint(11)NOT NULL AUTO_INCREMENT,titlevarchar(155)NOT NULL,imageURLvarchar(155)NOT NULL,mp3urlvarchar(155)NOT NULL,descriptiontext,lyrictext,albumvarchar(155)DEFAULT NULL,

Answer 1

尝试为artist_relations.mp3id、artist_relations.artistID和mp3s.id创建索引。请参见创建索引