mysql为什么这样的sql执行时不走索引

表结构为

CREATE TABLE `person` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) DEFAULT NULL,
  `address` varchar(255) DEFAULT NULL,
  `first_name` varchar(255) DEFAULT NULL,
  `tel` varchar(255) DEFAULT NULL,
  `job` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `name-address` (`name`,`address`,`first_name`)
) ENGINE=InnoDB AUTO_INCREMENT=16804 DEFAULT CHARSET=utf8;

现有执行计划不走索引

EXPLAIN SELECT * FROM person force index(`name-address`) WHERE `name` = 2 AND `address` LIKE "%222" and first_name LIKE "%222";

EXPLAIN SELECT * FROM person force index(`name-address`) WHERE `name` = 1 AND address = 1

执行计划为

最终解决结果

第一个不会走，第二个走，它与你用没用强制索引没有关系

LIKE "%xxx"这种情况是不走索引的
https://blog.csdn.net/shadow_zed/article/details/89117125

mysql最左匹配原则，左边的值不确定，不走索引，你的模糊查询%是一个不确定的值，所以不走索引

两条SQL可以走索引, 只要将name的值就是2和1改成字符串而不是数字, address也改字符串能用到更多的索引数据来过滤结果
EXPLAIN SELECT * FROM person force index(name-address) WHERE name = '2' AND address LIKE "%222" and first_name LIKE "%222";
EXPLAIN SELECT * FROM person force index(name-address) WHERE name = '1' AND address = '1'