我在mysql-slow.log中有以下条目：
# Time: 180506 21:57:03
# User@Host: mysqlserver[mysqlserver] @ localhost []
# Query_time: 88.963476 Lock_time: 0.000088 Rows_sent: 50 Rows_examined: 114197
SET timestamp=1525633023;
SELECT n1.full_name AS sender_full_name, s1.email AS sender_email, e.subject, e.body,
e.attach, e.date, e.id, r.status, n2.full_name AS receiver_full_name,
s2.email AS receiver_email, r.basket
FROM people_emails p
JOIN email_routing r ON r.receiver_email_id = 3223 AND r.status = 2
JOIN email e ON e.id = r.message_id
JOIN people_emails s1 ON s1.id = r.sender_email_id
JOIN people n1 ON n1.id = s1.people_id
JOIN people_emails s2 ON s2.id = r.receiver_email_id
JOIN people n2 ON n2.id = s2.people_id
WHERE p.internal_user_id = 314
ORDER BY e.date desc
LIMIT 0, 50;
该查询的结果类似于：
----------------------------------------------------------------------------------------------------
|sender_full_name|sender_email|subject|body| attach | date | id |status|receiver_full_name|basket|
----------------------------------------------------------------------------------------------------
|John Blow |jb@corp.lan |Aloha |Text| |180506|856050|2 |Mary Johns |1 |
----------------------------------------------------------------------------------------------------
以下是有关查询和使用的表的所有数据：
EXPLAIN SELECT n1.full_name AS sender_full_name, s1.email AS sender_email,
e.subject, e.body, e.attach, e.date, e.id, r.status, n2.full_name AS receiver_full_name,
s2.email AS receiver_email, r.basket, 'user777' FROM people_emails p
JOIN email_routing r ON r.receiver_email_id = 3233 AND r.status = 2
JOIN email e ON e.id = r.message_id
JOIN people_emails s1 ON s1.id = r.sender_email_id
JOIN people n1 ON n1.id = s1.people_id
JOIN people_emails s2 ON s2.id = r.receiver_email_id
JOIN people n2 ON n2.id = s2.people_id
WHERE p.internal_user_id = 314 ORDER BY e.date desc LIMIT 0, 50;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE s2 const PRIMARY PRIMARY 4 const 1 Using temporary; Using filesort
1 SIMPLE n2 const PRIMARY PRIMARY 4 const 1
1 SIMPLE p ALL NULL NULL NULL NULL 18631 Using where
1 SIMPLE r ALL NULL NULL NULL NULL 899567 Using where; Using join buffer
1 SIMPLE e eq_ref PRIMARY PRIMARY 4 server.r.message_id 1
1 SIMPLE s1 eq_ref PRIMARY PRIMARY 4 server.r.sender_email_id1
1 SIMPLE n1 eq_ref PRIMARY PRIMARY 4 server.s1.people_id 1
SHOW CREATE TABLE people_emails;
CREATE TABLE `people_emails` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`nick` varchar(255) NOT NULL,
`email` varchar(255) NOT NULL,
`key_name` varchar(255) NOT NULL,
`people_id` int(11) NOT NULL,
`status` int(11) NOT NULL DEFAULT '0',
`activity` int(11) NOT NULL,
`internal_user_id` int(11) NOT NULL,
PRIMARY KEY (`id`),
FULLTEXT KEY `email` (`email`)
) ENGINE=MyISAM AUTO_INCREMENT=22114 DEFAULT CHARSET=utf8
SHOW CREATE TABLE email_routing;
CREATE TABLE `email_routing` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`message_id` int(11) NOT NULL,
`sender_email_id` int(11) NOT NULL,
`receiver_email_id` int(11) NOT NULL,
`basket` int(11) NOT NULL,
`status` int(11) NOT NULL,
`popup` int(11) NOT NULL,
`tm` int(11) NOT NULL,
KEY `id` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=987389 DEFAULT CHARSET=utf8
SHOW CREATE TABLE email;
CREATE TABLE `email` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`subject` text NOT NULL,
`body` text NOT NULL,
`date` datetime NOT NULL,
`attach` text NOT NULL,
`attach_ondisk` text NOT NULL,
`attach_dir` varchar(255) CHARACTER SET cp1251 DEFAULT NULL,
`attach_subject` varchar(255) DEFAULT NULL,
`attach_content` longtext,
PRIMARY KEY (`id`),
KEY `Index_2` (`attach_dir`),
FULLTEXT KEY `path` (`attach_dir`)
) ENGINE=MyISAM AUTO_INCREMENT=856151 DEFAULT CHARSET=utf8
SHOW CREATE TABLE people;
CREATE TABLE `people` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`fname` varchar(255) CHARACTER SET cp1251 NOT NULL,
`lname` varchar(255) CHARACTER SET cp1251 NOT NULL,
`patronymic` varchar(255) CHARACTER SET cp1251 NOT NULL,
`gender` tinyint(1) NOT NULL,
`full_name` varchar(255) NOT NULL DEFAULT ' ',
`category` int(11) NOT NULL,
`people_type_id` int(255) DEFAULT NULL,
`tags` varchar(255) CHARACTER SET cp1251 NOT NULL,
`job` varchar(255) CHARACTER SET cp1251 NOT NULL,
`post` varchar(255) CHARACTER SET cp1251 NOT NULL,
`profession` varchar(255) CHARACTER SET cp1251 DEFAULT NULL,
`zip` varchar(16) CHARACTER SET cp1251 NOT NULL,
`country` int(11) DEFAULT NULL,
`region` varchar(10) NOT NULL,
`city` varchar(255) CHARACTER SET cp1251 NOT NULL,
`address` varchar(255) CHARACTER SET cp1251 NOT NULL,
`address_date` date DEFAULT NULL,
`inner` tinyint(4) NOT NULL,
`contact_through` varchar(255) DEFAULT '',
`next_call` date NOT NULL,
`additional` text CHARACTER SET cp1251 NOT NULL,
`user_id` int(11) NOT NULL,
`changed` datetime NOT NULL,
`status` int(11) DEFAULT NULL,
`nick` varchar(255) DEFAULT NULL,
`birthday` date DEFAULT NULL,
`last_update_ts` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
`area` text NOT NULL,
`reviewed_` tinyint(4) NOT NULL,
`phones_old` text NOT NULL,
`post_sticker` text NOT NULL,
`permissions` int(120) NOT NULL DEFAULT '0',
`internal_user_id` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `most_used` (`category`,`status`,`city`,`lname`,`next_call`),
KEY `registrars` (`category`,`status`,`contact_through`,`next_call`),
FULLTEXT KEY `lname` (`lname`),
FULLTEXT KEY `fname` (`fname`),
FULLTEXT KEY `mname` (`patronymic`),
FULLTEXT KEY `Full Name` (`full_name`)
) ENGINE=MyISAM AUTO_INCREMENT=415009 DEFAULT CHARSET=utf8
虽然根据评论的请求获得上述输出，但我也注意到我的表格都是不同的格式--MyISAM和InnoDB。这也可以成为问题的一部分吗？
我是否使表格结构过于复杂？我想了解查询的哪一部分使得这么慢，所以我可以重新安排我的表。
答案 0 :(得分：1)
通常，您希望从EXPLAIN报告中删除type=ALL中的条目。这意味着它正在进行表扫描，如果它发生在大型表上，这对性能有害。
在您的情况下，您有两个正在进行表扫描的表。检查解释，18631和899567的row列中的数字。将它们相乘= 16,759,832,777。这就是查询可能检查的行组合数量！
部分问题是您的查询正在执行Cartesian product。您没有条件将表p与其他表相关联。因此，对于p中检查的每一行，它将此与其他表中检查的行组合在一起。这成本很高。
目前还不清楚为什么你的查询中只有p，因为它与其他表无关，并且你不会在select-list中从中获取任何列。即使我从查询中取出p，我也可以生成您描述的结果集：
SELECT n1.full_name AS sender_full_name, s1.email AS sender_email,
e.subject, e.body, e.attach, e.date, e.id, r.status, n2.full_name AS receiver_full_name,
s2.email AS receiver_email, r.basket, 'user777'
FROM email_routing r
JOIN email e ON e.id = r.message_id
JOIN people_emails s1 ON s1.id = r.sender_email_id
JOIN people n1 ON n1.id = s1.people_id
JOIN people_emails s2 ON s2.id = r.receiver_email_id
JOIN people n2 ON n2.id = s2.people_id
WHERE r.receiver_email_id = 3233 AND r.status = 2
ORDER BY e.date desc LIMIT 0, 50;
我还建议添加这个索引：
ALTER TABLE email_routing ADD KEY bk1 (receiver_email_id, status,
sender_email_id, message_id, basket);
这有助于搜索r.receiver_email_id = 3233 AND r.status = 2。
附加列位于索引中，使其成为覆盖索引。这意味着如果查询从索引中获取了所需的所有列，则查询根本不必读取email_routing表。
此查询的EXPLAIN看起来更好，因为没有任何表正在执行type=ALL，其中一个表示“使用索引”，这是覆盖索引的指示符。
+----+-------------+-------+--------+---------------+---------+---------+------------------------+------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+---------------+---------+---------+------------------------+------+---------------------------------+
| 1 | SIMPLE | s2 | const | PRIMARY | PRIMARY | 4 | const | 1 | Using temporary; Using filesort |
| 1 | SIMPLE | n2 | const | PRIMARY | PRIMARY | 4 | const | 1 | NULL |
| 1 | SIMPLE | r | ref | bk1 | bk1 | 8 | const,const | 1 | Using index |
| 1 | SIMPLE | s1 | eq_ref | PRIMARY | PRIMARY | 4 | test.r.sender_email_id | 1 | NULL |
| 1 | SIMPLE | n1 | eq_ref | PRIMARY | PRIMARY | 4 | test.s1.people_id | 1 | NULL |
| 1 | SIMPLE | e | eq_ref | PRIMARY | PRIMARY | 4 | test.r.message_id | 1 | NULL |
+----+-------------+-------+--------+---------------+---------+---------+------------------------+------+---------------------------------+
P.S。：MyISAM与InnoDB对此查询优化几乎没有什么区别。该索引对两个存储引擎都有很大帮助。但我总是建议转换为InnoDB（参见我对MyISAM versus InnoDB的回答）。
答案 1 :(得分：1)
这看起来错误：
FROM people_emails p
JOIN email_routing r ON r.receiver_email_id = 3223
AND r.status = 2
p未在任何ON子句中使用。也许你错过了将p和r联系在一起的方式？没有它，你有一个＆＃34;交叉连接＆＃34;。如果每个行中有1K行，则最终会在连接中生成1M行。
另外，请使用ON来说明表格的相关性;使用WHERE进行过滤（3222＆amp; 2）。