mysql百万数据实践-索引

1.生成数据

//建表
CREATE TABLE `person` (
  `id` bigint(20) unsigned NOT NULL,
  `username` varchar(100) NOT NULL,
  `age` tinyint(3) unsigned NOT NULL,
  `sex` tinyint(1) unsigned NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

//创建生成数据procedure，num代表生成数据量的大小
CREATE PROCEDURE `generate`(IN num INT)  
BEGIN     
    DECLARE char_str varchar(100) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
    DECLARE username VARCHAR(25) DEFAULT '';    
    DECLARE id int UNSIGNED;  
    DECLARE len int;  
    set id=1;  
    DELETE from person;  
    WHILE id <= num DO  
        set len = FLOOR(1 + RAND()*25);  
        set username = '';  
        WHILE len > 0 DO  
            SET username = CONCAT(username,substring(char_str,FLOOR(1 + RAND()*62),1));  
            SET len = len - 1;  
        END WHILE;   
        INSERT into person VALUES (id,username, FLOOR(RAND()*100), FLOOR(RAND()*2));  
        set id = id + 1;  
    END WHILE;  
END 
//最后执行generate，生成100万数据
CALL generate(1000000);

 2.查询

select * from person ORDER BY username desc limit 100;

[SQL] SELECT * FROM person ORDER BY username DESC limit 100;
受影响的行: 0
时间: 3.900s

3.建立索引查询

create index index_user on person(username(100));

4.测试

 

 5.联合索引(复合索引)

例如索引是key index （a,b,c）。 可以支持a | a,b| a,b,c 3种组合进行查找，但不支持 b,c进行查找 

应该仔细考虑列的顺序。对索引中的所有列执行搜索或仅对前几列执行搜索时，复合索引非常有用；仅对后面的任意列执行搜索时，复合索引则没有用处。

参考：https://segmentfault.com/a/1190000012918964