使用 5 个左连接提高 MySQL 查询的速度

Question

正在开发支持票务系统，但票数不多（~3,000）。要获取票证信息的摘要网格，自定义字段 table (j25_field_value) 上有五个 LEFT JOIN 语句，包含大约 10,000 条记录。查询运行太长（~10 秒）并且在带有 WHERE 子句的情况下，它运行甚至更长（最多 ~30 秒或更多）。

关于改进查询以将时间减少到运行的任何建议？

四个table：

j25_support_tickets

CREATE TABLE `j25_support_tickets` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`category_id` int(11) NOT NULL DEFAULT '0',
`user_id` int(11) DEFAULT NULL,
`email` varchar(50) DEFAULT NULL,
`subject` varchar(255) DEFAULT NULL,
`message` text,
`modified_date` datetime DEFAULT NULL,
`priority_id` tinyint(3) unsigned DEFAULT NULL,
`status_id` tinyint(3) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `id` (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=3868 DEFAULT CHARSET=utf8

j25_support_priorities

CREATE TABLE `j25_support_priorities` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`title` varchar(100) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `id` (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=14 DEFAULT CHARSET=utf8

j25_support_statuses

CREATE TABLE `j25_support_statuses` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`title` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `id` (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=7 DEFAULT CHARSET=utf8

j25_field_value (id, ticket_id, field_id, field_value)

CREATE TABLE `j25_support_field_value` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`ticket_id` int(11) DEFAULT NULL,
`field_id` int(11) DEFAULT NULL,
`field_value` tinytext,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=10889 DEFAULT CHARSET=utf8

还有，运行这个：

    SELECT LENGTH(field_value) len FROM j25_support_field_value ORDER BY len DESC LIMIT 1
    note:  the result = 38

查询：

SELECT DISTINCT t.id as ID
, (select p.title from j25_support_priorities p where p.id = t.priority_id) as Priority
, (select s.title from j25_support_statuses   s where s.id = t.status_id)   as Status
,     t.subject       as Subject
,     t.email         as SubmittedByEmail
,  type.field_value   AS IssueType
,   ver.field_value   AS Version
, utype.field_value   AS UserType
,  cust.field_value   AS Company
, refno.field_value   AS RefNo
, t.modified_date     as Modified
    FROM j25_support_tickets AS t
LEFT JOIN j25_support_field_value AS type  ON t.id = type.ticket_id  AND  type.field_id =1
LEFT JOIN j25_support_field_value AS ver   ON t.id = ver.ticket_id   AND   ver.field_id =2
LEFT JOIN j25_support_field_value AS utype ON t.id = utype.ticket_id AND utype.field_id =3
LEFT JOIN j25_support_field_value AS cust  ON t.id = cust.ticket_id  AND  cust.field_id =4
LEFT JOIN j25_support_field_value AS refno ON t.id = refno.ticket_id AND refno.field_id =5

Answer 1

您可以取消 starters 的子查询，只从另一个连接中获取它们。您可以添加索引 j25_support_field_value

alter table j25_support_field_value add key(id, field_type);

我假设 j25_support_tickets 中的 id 有一个索引 - 如果没有并且它们是唯一的，请添加一个唯一索引 alter table j25_support_tickets add unique key(id); 如果它们不是唯一的，请从中删除唯一这个词声明。

在 MySQL 中，联接通常需要您用于联接的字段的索引。这将适用于巨大的表（100m+）并产生非常合理的结果，如果你遵循这个规则，你就不会出错。

j25_support_tickets 中的 ID 是否唯一？如果他们是你可以取消不同 - 如果不是，或者如果你在每一行中得到精确的重复，仍然取消不同并添加一个 t.id 到这个末尾的组：

SELECT t.id as ID
, p.title  as Priority
, s.title as Status
,     t.subject       as Subject
,     t.email         as SubmittedByEmail
,  type.field_value   AS IssueType
,   ver.field_value   AS Version
, utype.field_value   AS UserType
,  cust.field_value   AS Company
, refno.field_value   AS RefNo
, t.modified_date     as Modified
    FROM  j25_support_tickets AS t
LEFT JOIN j25_support_field_value AS type  ON t.id = type.ticket_id  AND  type.field_id =1
LEFT JOIN j25_support_field_value AS ver   ON t.id = ver.ticket_id   AND   ver.field_id =2
LEFT JOIN j25_support_field_value AS utype ON t.id = utype.ticket_id AND utype.field_id =3
LEFT JOIN j25_support_field_value AS cust  ON t.id = cust.ticket_id  AND  cust.field_id =4
LEFT JOIN j25_support_field_value AS refno ON t.id = refno.ticket_id AND refno.field_id =5
LEFT JOIN j25_support_priorities p ON p.id = t.priority_id
LEFT JOIN j25_support_statuses  s ON s.id = t.status_id;

Answer 2

ALTER TABLE j25_support_field_value
ADD INDEX (`ticket_id`,`field_id`,`field_value`(50))

该索引将作为您查询的覆盖索引。它将允许连接仅使用该索引来查找值。它的执行速度应该比没有此索引快得多，因为目前您的查询必须读取 table 中的每一行才能找到与 ticket_id 和 field_id.[=14= 的每个组合相匹配的内容]

我还建议将您的 table 转换为 InnoDB 引擎，除非您有非常明确的理由使用 MyISAM。

ALTER TABLE tablename ENGINE=InnoDB

Answer 3

同上 - 更好的索引会有所帮助。然后，您可能也可以将查询简化为类似的内容（仅加入 table 一次）：

SELECT t.id as ID
, p.title  as Priority
, s.title as Status
,     t.subject       as Subject
,     t.email         as SubmittedByEmail
, case when v.field_id=1 then v.field_value else null end as IssueType
, case when v.field_id=2 then v.field_value else null end as Version
, case when v.field_id=3 then v.field_value else null end as UserType
, case when v.field_id=4 then v.field_value else null end as Company
, case when v.field_id=5 then v.field_value else null end as RefNo
 , t.modified_date     as Modified
    FROM  j25_support_tickets AS t
LEFT JOIN j25_support_field_value v ON t.id = v.ticket_id
LEFT JOIN j25_support_priorities p ON p.id = t.priority_id
LEFT JOIN j25_support_statuses  s ON s.id = t.status_id;

Answer 4

切换到 InnoDB。
切换到 InnoDB 后，使 j25_support_field_value 的 PRIMARY KEY 为 (ticket_id, field_id)（如果 id 则删除） . （攻击 field_value(50) 会很痛，不会有帮助。）
一个 PRIMARY KEY 是一个 UNIQUE KEY，所以不要两者都有。
使用 VARCHAR(255) 而不是几乎等价的 TINYTEXT。
EAV 架构糟透了。 My ran on EAV.

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