Mysql
 sql >> база данни >  >> RDS >> Mysql

Пренаписване на mysql select за намаляване на времето и запис на tmp на диск

надявам се да намерите това за полезно - 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


  1. Database
  2.   
  3. Mysql
  4.   
  5. Oracle
  6.   
  7. Sqlserver
  8.   
  9. PostgreSQL
  10.   
  11. Access
  12.   
  13. SQLite
  14.   
  15. MariaDB
  1. MySQL синтаксис за Join Update

  2. Инсталиране на MySQL JDBC драйвери в Pentaho Data Integration и BA Server инструменти

  3. MySQL 8 Общи изрази за таблица CTE

  4. PostgreSQL срещу MySQL, сравнение

  5. MySQL - Как да търся точно съвпадение на думи с LIKE?