我的问题。我想我有一个性能杀伤子查询,但无法证明它。我第一次尝试使用 JOIN 失败了。有人可以提供更高性能的解决方案或确认这确实可以接受吗?
我有两张表,一张包含待办事项列表(joblist),一张跟踪每个用户的进度(userprogress)。工作可以但不能是看视频。(这是一个电子学习网站。)
观看视频后,它们会在枚举字段上自动设置为“已完成”。用户也可以手动跳过视频(status = 'skipped')。
下面提供了表结构。
要获取用户根本没有观看的第一个视频(用户进度中没有记录)或已经开始观看(状态 = '开始'),我正在使用此查询。
我已经在用于选择或排序的任何字段上设置了索引。但是我不确定它们是否都需要。
SELECT 语句有两个部分
- 一个内部子选择,我在其中获取所有看过或跳过的视频
- 主要声明,我在其中获取第一个视频,而不是(1)找到的视频
PHP (:email) 有一个命名参数,以避免 SQL 注入。
SELECT jl.where_to_do_it FROM joblist AS jl
INNER JOIN userprogress AS up
ON (jl.joblistID = up.joblistID)
WHERE jl.what_to_do = 'video'
AND jl.joblistID NOT IN
(
SELECT injl.joblistID
FROM joblist AS injl
INNER JOIN userprogress AS inup
ON (injl.joblistID = inup.joblistID)
WHERE
(inup.status = 'finished' OR inup.status = 'skipped')
AND
inup.email = :email
AND
injl.what_to_do = 'video'
)
ORDER BY jl.joborder ASC
LIMIT 0,1
这是 EXPLAIN 的输出,我需要一些帮助来理解。
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY jl ref PRIMARY,what_to_do what_to_do 602 const 9 Using where; Using filesort
1 PRIMARY up ref joblistID joblistID 3 jl.joblistID 1 Using index
2 DEP-SUB injl eq_ref PRIMARY,what_to_do PRIMARY 3 func 1 Using where
2 DEP-SUB inup eq_ref nodup,email,joblistID,status nodup 455 const,func 1 Using where
创建表命令:
CREATE TABLE IF NOT EXISTS `joblist` (
`joblistID` mediumint(10) unsigned NOT NULL AUTO_INCREMENT,
`what_to_do` varchar(200) COLLATE utf8_swedish_ci NOT NULL,
`where_to_do_it` varchar(100) COLLATE utf8_swedish_ci NOT NULL,
`joborder` mediumint(6) NOT NULL,
`track` enum('fast','slow','bonus') COLLATE utf8_swedish_ci NOT NULL DEFAULT 'slow',
`chapter` tinyint(11) unsigned NOT NULL COMMENT 'What book chapter it relates to',
PRIMARY KEY (`joblistID`),
KEY `nodupjobs` (`joborder`,`chapter`),
KEY `what_to_do` (`what_to_do`),
KEY `where_to_do_it` (`where_to_do_it`),
KEY `joborder` (`joborder`),
KEY `track` (`track`),
KEY `chapter` (`chapter`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_swedish_ci COMMENT='Suggested working order';
CREATE TABLE IF NOT EXISTS `userprogress` (
`upID` int(10) unsigned NOT NULL AUTO_INCREMENT,
`email` varchar(150) COLLATE utf8_swedish_ci NOT NULL COMMENT 'user id',
`joblistID` mediumint(9) unsigned NOT NULL COMMENT 'foreign key',
`progressdata` varchar(300) COLLATE utf8_swedish_ci DEFAULT NULL COMMENT 'JSON object describing progress',
`percentage_complete` tinyint(3) unsigned DEFAULT NULL,
`status` enum('begun','skipped','finished') COLLATE utf8_swedish_ci DEFAULT 'begun',
`lastupdate` datetime NOT NULL,
`approved` datetime DEFAULT NULL,
PRIMARY KEY (`upID`),
UNIQUE KEY `nodup` (`email`,`joblistID`),
KEY `email` (`email`),
KEY `joblistID` (`joblistID`),
KEY `status` (`status`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_swedish_ci COMMENT='Keep track of what the user has done';