hy vọng bạn thấy điều này hữu ích - 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
