索引

作用

• 提高查询速度
  
• 确保数据的唯一性
  
• 可以加速表和表之间的连接 , 实现表与表之间的参照完整性
  
• 使用分组和排序子句进行数据检索时 , 可以显著减少分组和排序的时间
  

• 全文检索字段进行搜索优化.
  

  分类

• 主键索引 (Primary Key)

• 唯一索引 (Unique)
  
• 常规索引 (Index)
  
• 全文索引 (FullText)

100w条数据测试

建表

CREATE TABLE `app_user` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(50) DEFAULT '' COMMENT '用户昵称',
  `email` varchar(50) NOT NULL COMMENT '用户邮箱',
  `phone` varchar(20) DEFAULT '' COMMENT '手机号',
  `gender` tinyint(4) unsigned DEFAULT '0' COMMENT '性别（0:男；1：女）',
  `password` varchar(100) NOT NULL COMMENT '密码',
  `age` tinyint(4) DEFAULT '0' COMMENT '年龄',
  `create_time` datetime DEFAULT CURRENT_TIMESTAMP,
  `update_time` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='app用户表'

插入数据

DROP FUNCTION IF EXISTS mock_data;
DELIMITER $$
CREATE FUNCTION mock_data()
RETURNS INT
BEGIN
  DECLARE num INT DEFAULT 1000000;
  DECLARE i INT DEFAULT 0;
  WHILE i < num DO
   INSERT INTO app_user(`name`, `email`, `phone`, `gender`, `password`, `age`)
    VALUES(CONCAT('用户', i), '24736743@qq.com', CONCAT('18', FLOOR(RAND()*(999999999-100000000)+100000000)),FLOOR(RAND()*2),UUID(), FLOOR(RAND()*100));
   SET i = i + 1;
  END WHILE;
  RETURN i;
END;
SELECT mock_data();

索引效率测试
无索引

SELECT * FROM app_user WHERE name = '用户9999'; -- 查看耗时
SELECT * FROM app_user WHERE name = '用户9999';
SELECT * FROM app_user WHERE name = '用户9999';

mysql> EXPLAIN SELECT * FROM app_user WHERE name = '用户9999'\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: app_user
   partitions: NULL
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 992759
     filtered: 10.00
        Extra: Using where
1 row in set, 1 warning (0.00 sec)

创建索引

CREATE INDEX idx_app_user_name ON app_user(name);

测试普通索引

mysql> EXPLAIN SELECT * FROM app_user WHERE name = '用户9999'\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: app_user
   partitions: NULL
         type: ref
possible_keys: idx_app_user_name
          key: idx_app_user_name
      key_len: 203
          ref: const
         rows: 1
     filtered: 100.00
        Extra: NULL
1 row in set, 1 warning (0.00 sec)

mysql> SELECT * FROM app_user WHERE name = '用户9999';
1 row in set (0.00 sec)

mysql> SELECT * FROM app_user WHERE name = '用户9999';
1 row in set (0.00 sec)

mysql> SELECT * FROM app_user WHERE name = '用户9999';
1 row in set (0.00 sec)