mysql中能够使用索引的典型场景

Posted 2020-09-25 心碎whn

mysql 演示数据库：http://downloads.mysql.com/docs/sakila-db.zip

匹配全值

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explain select * from rental where rental_date=\'2005-05-25 17:22:10\' and inventory_id=373 and customer_id=343

 

 

匹配值的范围查询

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explain select * from rental where customer_id >= 373 and customer_id<400

 

 

匹配最左前缀

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仅仅使用索引中的最左列进行查询，比如：在col1+col2+col3字段上的联合索引中，能够使用的索引情况可以有：col1 (col2+col3) ,col1+col2+col3。不能被使用的索引：col2 (col2+col3) 等情况。以payment表为例

 

alter table payment add index idx_payment_date (payment_date,amount,last_update);

 

 

 

explain select * from payment where payment_date=\'2006-02-14 15:16:03\' and last_update=\'2006-02-15 22:12:32\'\\G;

 

 

 explain select * from payment where amount=3.98 and last_update=\'2006-02-15 22:12:32\'\\G;

 

 

explain select * from payment where amount=3.98 and payment_date=\'2006-02-14 15:16:03\'\\G;

 

 

explain select * from payment where last_update=\'2006-02-15 22:12:32\' and payment_date=\'2006-02-14 15:16:03\'\\G;

 

 

 仅仅对索引进行查询

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 当查询的的列都在索引的字段中时，查询的效率更高

explain select last_update from payment where amount=3.98\\G;

 

 

explain select last_update from payment where payment_date=\'2006-02-14 15:16:03\'\\G;

 

 

匹配列前缀

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仅仅使用索引中的第一列，并且只包含索引第一列的开头一部分进行查找

 

explain select title from film_text where title like \'AFRICAN%\'\\G;

 

 

 explain select description from film_text where description like \'AFRICAN%\'\\G;

 

 

 如果列名是索引，那么使用column_name is null 就会使用索引

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explain select * from payment where rental_id is null\\G;

 

 

 

实现索引匹配部分精确而其他部分进行范围匹配

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explain select inventory_id from rental where rental_date=\'2006-02-14 15:16:03\' and customer_id>=300 and customer_id<=400\\G;

 

 

Index Condition PushDown(ICP)

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mysql 5.6引入了Index Condition PushDown(ICP) 的特性，进一步优化了查询，某些情况下的条件过滤操作下放到存储引擎

 

explain select * from rental where rental_date=\'2006-02-14 15:16:03\' and customer_id>=300 and customer_id<=400\\G;

 

 

5.5版本的复合索引

 

 

5.6版本的ICP