MySQL索引的学习和研究
这里所谈论只针对B-Tree类型索引，也是MySQL用的最多最普通的索引。建立索引的时候是按照字面量的顺序建立的，这个要特别注意。在B-Tree类型索引中，索引顺序是相当重要的。mysql
高性能索引
-
索引要小而美sql
-
单列索引数据库
-
前缀索引函数
-
多列索引性能
-
选择合适的索引顺序.net
-
覆盖索引code
-
使用索引扫描来排序orm
首先构造1亿条数据
参照前面写的文章造数据blog
http://blog.csdn.net/csujiangyu/article/details/51096978排序
索引结构以下
mysql> show index from user; +-------+------------+-------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +-------+------------+-------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | user | 0 | PRIMARY | 1 | id | A | 92123632 | NULL | NULL | | BTREE | | | | user | 1 | idx_last_first_name_age | 1 | last_name | A | 363474 | NULL | NULL | YES | BTREE | | | | user | 1 | idx_last_first_name_age | 2 | first_name | A | 92123840 | NULL | NULL | YES | BTREE | | | | user | 1 | idx_last_first_name_age | 3 | age | A | 87360984 | NULL | NULL | YES | BTREE | | | | user | 1 | idx_phone | 1 | phone | A | 92123840 | NULL | NULL | YES | BTREE | | | | user | 1 | idx_create_time | 1 | create_time | A | 88503 | NULL | NULL | YES | BTREE | | | +-------+------------+-------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 6 rows in set (0.00 sec)
user表一共有4个索引，包括一个主键id，2个单列索引(phone, create_time), 1个多列索引(last_name+first_name+age)
经过explain来查看使用索引状况
主要关注以下：
-
type：访问类型，性能从差到好为：
ALL -> index -> range -> ref -> eq_ref -> const,system -> NULL
-
index：使用的索引
能够使用索引的状况
单列索引全值匹配
这是最简单的方式
mysql> explain SELECT * from user where phone = '13901986429'; +----+-------------+-------+------------+------+---------------+-----------+---------+-------+------+----------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+-----------+---------+-------+------+----------+-------+ | 1 | SIMPLE | user | NULL | ref | idx_phone | idx_phone | 14 | const | 1 | 100.00 | NULL | +----+-------------+-------+------------+------+---------------+-----------+---------+-------+------+----------+-------+ 1 row in set, 1 warning (0.01 sec)
从type能够得知访问类型ref，使用索引key为idx_phone。
多列索引全值匹配
mysql> explain SELECT * FROM user where last_name='last_name_110' and first_name='first_name_115' and sex='F'; +----+-------------+-------+------------+------+-------------------------+-------------------------+---------+-------------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+-------------------------+-------------------------+---------+-------------+------+----------+-------------+ | 1 | SIMPLE | user | NULL | ref | idx_last_first_name_age | idx_last_first_name_age | 96 | const,const | 1 | 10.00 | Using where | +----+-------------+-------+------------+------+-------------------------+-------------------------+---------+-------------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)
前缀索引
若是是单列索引，能够匹配列的最左前缀
mysql> explain SELECT * from user where phone like '139019864%'; +----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-----------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-----------------------+ | 1 | SIMPLE | user | NULL | range | idx_phone | idx_phone | 14 | NULL | 100 | 100.00 | Using index condition | +----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-----------------------+ 1 row in set, 1 warning (0.01 sec)
若是是多列索引，能够从左开始组合索引
mysql> explain SELECT * FROM user where last_name='last_name_110' and first_name='first_name_115'; +----+-------------+-------+------------+------+-------------------------+-------------------------+---------+-------------+------+----------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+-------------------------+-------------------------+---------+-------------+------+----------+-------+ | 1 | SIMPLE | user | NULL | ref | idx_last_first_name_age | idx_last_first_name_age | 96 | const,const | 1 | 100.00 | NULL | +----+-------------+-------+------------+------+-------------------------+-------------------------+---------+-------------+------+----------+-------+ 1 row in set, 1 warning (0.01 sec)
匹配索引值的范围
使用between
mysql> explain select * from user where id between 1 and 10; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | 1 | SIMPLE | user | NULL | range | PRIMARY | PRIMARY | 4 | NULL | 10 | 100.00 | Using where | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)
使用in
mysql> explain select * from user where id in (1, 2, 3); +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | 1 | SIMPLE | user | NULL | range | PRIMARY | PRIMARY | 4 | NULL | 3 | 100.00 | Using where | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.01 sec)
使用or
mysql> explain select * from user where id=1 or id=10; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | 1 | SIMPLE | user | NULL | range | PRIMARY | PRIMARY | 4 | NULL | 2 | 100.00 | Using where | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)
覆盖索引
Extra字段为Using index，能够看出返回数据只须要查索引便可，不须要回表查其余字段数据。
mysql> explain select phone from user where phone='13900123456'; +----+-------------+-------+------------+------+---------------+-----------+---------+-------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+-----------+---------+-------+------+----------+-------------+ | 1 | SIMPLE | user | NULL | ref | idx_phone | idx_phone | 14 | const | 1 | 100.00 | Using index | +----+-------------+-------+------------+------+---------------+-----------+---------+-------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)
不能使用索引的状况
从type为ALL能够看出进行了全表扫描。
没有使用左前缀索引
phone是索引列，格式为’%XXX’不能是使用索引
mysql> explain SELECT * from user where phone like '%39019864%'; +----+-------------+-------+------------+------+---------------+------+---------+------+---------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+---------+----------+-------------+ | 1 | SIMPLE | user | NULL | ALL | NULL | NULL | NULL | NULL | 9698255 | 11.11 | Using where | +----+-------------+-------+------------+------+---------------+------+---------+------+---------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)
没有采用最左组合索引
last_name + first_name + sex联合组成了多列索引，采用最左匹配， 只有last_name，last_name + first_name，last_name + first_name + sex才能使用索引。
mysql> explain SELECT * FROM user where first_name='first_name_115' and sex='F'; +----+-------------+-------+------------+------+---------------+------+---------+------+---------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+---------+----------+-------------+ | 1 | SIMPLE | user | NULL | ALL | NULL | NULL | NULL | NULL | 9698255 | 1.00 | Using where | +----+-------------+-------+------------+------+---------------+------+---------+------+---------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)
使用函数
mysql> explain SELECT * FROM user where left(phone, 11) = '13900123456'; +----+-------------+-------+------------+------+---------------+------+---------+------+---------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+---------+----------+-------------+ | 1 | SIMPLE | user | NULL | ALL | NULL | NULL | NULL | NULL | 9698255 | 100.00 | Using where | +----+-------------+-------+------------+------+---------------+------+---------+------+---------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)
用索引字段进行计算
mysql> explain select * from user where id + 1 = 2; +----+-------------+-------+------------+------+---------------+------+---------+------+----------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+----------+----------+-------------+ | 1 | SIMPLE | user | NULL | ALL | NULL | NULL | NULL | NULL | 92123838 | 100.00 | Using where | +----+-------------+-------+------------+------+---------------+------+---------+------+----------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)
or后面没有使用索引
mysql> explain select * from user where id=1 or age=10; +----+-------------+-------+------------+------+---------------+------+---------+------+----------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+----------+----------+-------------+ | 1 | SIMPLE | user | NULL | ALL | PRIMARY | NULL | NULL | NULL | 92123838 | 10.00 | Using where | +----+-------------+-------+------------+------+---------------+------+---------+------+----------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)
索引和数据占用空间的查询
-- 查看example数据库总体大小 SELECT CONCAT(table_schema,'.',table_name) AS 'Table Name', CONCAT(ROUND(table_rows/1000000,4),'M') AS 'Number of Rows', CONCAT(ROUND(data_length/(1024*1024*1024),4),'G') AS 'Data Size', CONCAT(ROUND(index_length/(1024*1024*1024),4),'G') AS 'Index Size', CONCAT(ROUND((data_length+index_length)/(1024*1024*1024),4),'G') AS'Total'FROM information_schema.TABLES WHERE table_schema = 'example';
从图能够看出，1亿条数据索引占用了9.69G，数据占用了10G，总共占用了将近20G。索引占用空间几乎和数据大小同样，所以咱们须要慎用索引，在必要的状况下才使用，索引要小而美。
相关文章
- 1. oracle索引研究
- 2. ZMQ的学习和研究
- 3. MySQL索引深究
- 4. Mysql索引学习
- 5. MySQL索引学习
- 6. mysql索引学习
- 7. MySQL学习 - 索引
- 8. mysql学习-索引
- 9. mysql 索引的探究
- 10. Mysql 索引的学习
- 更多相关文章...
- • MySQL索引简介 - MySQL教程
- • MySQL修改和删除索引（DROP INDEX） - MySQL教程
- • 适用于PHP初学者的学习线路和建议
- • 漫谈MySQL的锁机制
相关标签/搜索
每日一句
-
每一个你不满意的现在，都有一个你没有努力的曾经。
最新文章
- 1. 「插件」Runner更新Pro版，帮助设计师远离996
- 2. 错误 707 Could not load file or assembly ‘Newtonsoft.Json, Version=12.0.0.0, Culture=neutral, PublicKe
- 3. Jenkins 2018 报告速览，Kubernetes使用率跃升235%！
- 4. TVI-Android技术篇之注解Annotation
- 5. android studio启动项目
- 6. Android的ADIL
- 7. Android卡顿的检测及优化方法汇总（线下+线上）
- 8. 登录注册的业务逻辑流程梳理
- 9. NDK(1)创建自己的C/C++文件
- 10. 小菜的系统框架界面设计-你的评估是我的决策
欢迎关注本站公众号,获取更多信息
相关文章
- 1. oracle索引研究
- 2. ZMQ的学习和研究
- 3. MySQL索引深究
- 4. Mysql索引学习
- 5. MySQL索引学习
- 6. mysql索引学习
- 7. MySQL学习 - 索引
- 8. mysql学习-索引
- 9. mysql 索引的探究
- 10. Mysql 索引的学习