[英]mysql query optimization - join and orderby
我需要一个mysql查询优化的帮助。 这是一个简单的查询,但是任何不正确的操作我都找不到:-(
我有2个表格:产品(> 40000行)和product_tags(> 500万)
表1-> N之间有一个关系。 每个产品在表产品标签中可以有许多标签。
我有这个简单的查询:
EXPLAIN SELECT t.product_id, kwt.tag_id
FROM products AS t, product_tags AS kwt
WHERE 1
AND t.product_id = kwt.product_id
AND kwt.tag_id =11
ORDER BY t.order_date
wchich返回55个结果。
第一种情况:如果我具有以下表格的表格结构:
CREATE TABLE IF NOT EXISTS `products` (
`product_id` int(10) unsigned NOT NULL auto_increment,
`product_source_id` smallint(5) unsigned NOT NULL,
`order_date` int(10) unsigned NOT NULL,
PRIMARY KEY (`product_id`),
KEY `order_date` (`order_date`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ;
CREATE TABLE IF NOT EXISTS `product_tags` (
`product_tag_id` int(10) unsigned NOT NULL auto_increment,
`tag_id` int(10) unsigned NOT NULL,
`product_id` int(11) NOT NULL,
PRIMARY KEY (`product_tag_id`),
KEY `product_id` (`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ;
那么查询的解释是这样的:
+----+-------------+-------+-------+---------------+------------+---------+---------------------------+-------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+------------+---------+---------------------------+-------+-------------+
| 1 | SIMPLE | t | index | PRIMARY | order_date | 4 | NULL | 45392 | Using index |
| 1 | SIMPLE | kwt | ref | product_id | product_id | 4 | t.product_id | 3 | Using where |
+----+-------------+-------+-------+---------------+------------+---------+---------------------------+-------+-------------+
它从表产品获取所有行,但是临时表没有任何内容。
第二种情况:如果我在product_tags中为“ tag_id”字段添加索引,则图片将有所不同:
+----+-------------+-------+--------+-------------------+---------+---------+-----------------------------+------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+-------------------+---------+---------+-----------------------------+------+---------------------------------+
| 1 | SIMPLE | kwt | ref | product_id,tag_id | tag_id | 4 | const | 55 | Using temporary; Using filesort |
| 1 | SIMPLE | t | eq_ref | PRIMARY | PRIMARY | 4 | kwt.product_id | 1 | Using where |
+----+-------------+-------+--------+-------------------+---------+---------+-----------------------------+------+---------------------------------+
现在它只选择55行,没错,但是查询很复杂:(
我的错在哪里?
谢谢尼克
这就是我会做的:
http://dev.mysql.com/doc/refman/5.0/en/innodb-index-types.html
http://www.xaprb.com/blog/2006/07/04/how-to-exploit-mysql-index-optimizations/
简化架构:
drop table if exists products;
create table products
(
prod_id int unsigned not null auto_increment primary key,
name varchar(255) not null unique
)
engine = innodb;
drop table if exists tags;
create table tags
(
tag_id mediumint unsigned not null auto_increment primary key,
name varchar(255) not null unique
)
engine = innodb;
drop table if exists product_tags;
create table product_tags
(
tag_id mediumint unsigned not null,
prod_id int unsigned not null,
created_date date not null,
primary key (tag_id, prod_id), -- note the clustered composite index and the order !!
key (prod_id)
)
engine = innodb;
select
pt.tag_id,
pt.prod_id
from
product_tags pt
inner join products p on pt.prod_id = p.prod_id
where
pt.tag_id = 11
order by
pt.created_date
limit 10;
我什至可以将product_tags PK更改为主键(tag_id,prod_id,created_date),但这全都取决于您运行的典型查询。 如果您认为可以提高性能,则可以在创建日期创建一个非聚集二级索引。
希望这可以帮助 :)
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