重写mysql select以减少时间并将tmp写入磁盘 [英] Rewriting mysql select to reduce time and writing tmp to disk

问题描述

我有一个耗时数分钟的mysql查询，因为它是用来创建网页的，所以效果不是很好.

I have a mysql query that's taking several minutes which isn't very good as it's used to create a web page.

使用三个表:poster_data包含有关单个海报的信息. poster_categories列出所有类别(电影，艺术品等)，而poster_prodcat列出后继编号及其可能位于的类别.一张海报将包含多行内容，例如电影，印第安纳·琼斯，哈里森·福特，冒险电影等.

Three tables are used: poster_data contains information on individual posters. poster_categories lists all the categories (movies, art, etc) while poster_prodcat lists the posterid number and the categories it can be in e.g. one poster would have multiple lines for say, movies, indiana jones, harrison ford, adventure films, etc.

这是慢速查询:

select * 
  from poster_prodcat, 
       poster_data, 
       poster_categories 
 where poster_data.apnumber = poster_prodcat.apnumber 
   and poster_categories.apcatnum = poster_prodcat.apcatnum 
   and poster_prodcat.apcatnum='623'  
ORDER BY aptitle ASC 
   LIMIT 0, 32

根据说明:

这花了几分钟. Poster_data的行数刚好超过80万，而poster_prodcat的行数刚好超过1700万.带有此选择的其他类别查询几乎没有引起注意，而poster_prodcat.apcatnum ='623'大约有40万个结果，并且正在写到磁盘上

It was taking a few minutes. Poster_data has just over 800,000 rows, while poster_prodcat has just over 17 million. Other category queries with this select are barely noticeable, while poster_prodcat.apcatnum='623' has about 400,000 results and is writing out to disk

推荐答案

希望对您有所帮助- http://pastie .org/1105206

drop table if exists poster;
create table poster
(
poster_id int unsigned not null auto_increment primary key,
name varchar(255) not null unique
)
engine = innodb; 


drop table if exists category;
create table category
(
cat_id mediumint unsigned not null auto_increment primary key,
name varchar(255) not null unique
)
engine = innodb; 

drop table if exists poster_category;
create table poster_category
(
cat_id mediumint unsigned not null,
poster_id int unsigned not null,
primary key (cat_id, poster_id) -- note the clustered composite index !!
)
engine = innodb;

-- FYI http://dev.mysql.com/doc/refman/5.0/en/innodb-index-types.html

select count(*) from category
count(*)
========
500,000


select count(*) from poster
count(*)
========
1,000,000

select count(*) from poster_category
count(*)
========
125,675,688

select count(*) from poster_category where cat_id = 623
count(*)
========
342,820

explain
select
 p.*,
 c.*
from
 poster_category pc
inner join category c on pc.cat_id = c.cat_id
inner join poster p on pc.poster_id = p.poster_id
where
 pc.cat_id = 623
order by
 p.name
limit 32;

id  select_type table   type    possible_keys   key     key_len ref                         rows
==  =========== =====   ====    =============   ===     ======= ===                         ====
1   SIMPLE      c       const   PRIMARY         PRIMARY 3       const                       1   
1   SIMPLE      p       index   PRIMARY         name    257     null                        32  
1   SIMPLE      pc      eq_ref  PRIMARY         PRIMARY 7       const,foo_db.p.poster_id    1   

select
 p.*,
 c.*
from
 poster_category pc
inner join category c on pc.cat_id = c.cat_id
inner join poster p on pc.poster_id = p.poster_id
where
 pc.cat_id = 623
order by
 p.name
limit 32;

Statement:21/08/2010 
0:00:00.021: Query OK

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