我的 SQL 查询有问题,有什么办法可以加快这个查询的速度吗? 表字包含 14000 行查询在本地主机上花费了 4.5631 秒。
SELECT
(SELECT SUM((SELECT COUNT(*)
FROM word w
WHERE w.lecture_id = l._id AND active = 1))
FROM lecture l
WHERE l.book_id = b._id) AS active_word_count,
(SELECT SUM((SELECT COUNT(*)
FROM word w
WHERE w.lecture_id = l._id))
FROM lecture l
WHERE book_id = b._id) AS word_count,
(SELECT COUNT(*)
FROM lecture l
WHERE l.book_id = b._id) AS lecture_count,
b._id,
b.name,
b.version
FROM book b
CREATE TABLE book (
_id int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
version tinyint(3) unsigned NOT NULL,
lang tinyint(4) NOT NULL DEFAULT '1',
PRIMARY KEY (_id)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=21 ;
CREATE TABLE lecture (
_id int(11) NOT NULL AUTO_INCREMENT,
book_id int(11) NOT NULL,
lecture_name varchar(255) NOT NULL,
PRIMARY KEY (_id)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=155 ;
CREATE TABLE word (
_id int(11) NOT NULL AUTO_INCREMENT,
question varchar(255) NOT NULL,
answer varchar(255) NOT NULL,
active tinyint(1) NOT NULL,
lecture_id int(11) NOT NULL,
PRIMARY KEY (_id)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;
查询返回数据,女巫在这里可用:http://pastebin.com/80KNsU7Y
谢谢你的帮助。
最佳答案
我已经添加了几个索引,它们将加速以这种方式编写的查询。他们也可能会帮助处理原件。 http://sqlfiddle.com/#!2/bdcf8/1
Select
Sum(Case When w.Active = 1 Then 1 Else 0 End) As active_word_count,
Count(w._id) As word_count,
Count(Distinct l._id) As lecture_count,
b._id,
b.name,
b.version
From
Book b
Left Outer Join
Lecture l
On l.book_id = b._id
Left Outer Join
Word w
On w.lecture_id = l._id
Group By
b._id,
b.name,
b.version
关于mysql - 内部 SQL 查询优化,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13343698/