MySQL隐式类型转换导致索引失效

今天发现一个问题，where条件的列上明明有索引，但是执行计划还是走全表扫描

mysql>  explain select task_id FROM mostop_xiaodai_collection_call_auto WHERE task_id = 433423882127424 AND task_data_id = 27739131157286912;+----+-------------+-------------------------------------+------------+------+------------------------------+------+---------+------+---------+----------+-------------+| id | select_type | table                               | partitions | type | possible_keys                | key  | key_len | ref  | rows    | filtered | Extra       |+----+-------------+-------------------------------------+------------+------+------------------------------+------+---------+------+---------+----------+-------------+|  1 | SIMPLE      | mostop_xiaodai_collection_call_auto | NULL       | ALL  | IDX_task_id,IDX_task_data_id | NULL | NULL    | NULL | 3101134 |     1.00 | Using where |+----+-------------+-------------------------------------+------------+------+------------------------------+------+---------+------+---------+----------+-------------+1 row in set, 5 warnings (0.00 sec)

查看表结构

mysql> show create table mostop_xiaodai_collection_call_auto\G*************************** 1. row ***************************       Table: mostop_xiaodai_collection_call_autoCreate Table: CREATE TABLE `mostop_xiaodai_collection_call_auto` (  `id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT '编号',  `agentid` int(10) unsigned NOT NULL COMMENT '渠道 ID',  `loan_id` bigint(20) unsigned NOT NULL DEFAULT '0' COMMENT '借款 ID',  `user_id` bigint(20) unsigned NOT NULL COMMENT '借款人 ID',  `call_mobile` varchar(20) NOT NULL COMMENT '手机号',  `call_name` varchar(20) NOT NULL COMMENT '名称',  `call_sex` varchar(20) NOT NULL COMMENT '性别',  `call_due_date` date NOT NULL COMMENT '应还日期',  `call_overdue_day` int(10) NOT NULL COMMENT '逾期天数（负数为贷前催告的天数）',  `call_talking_type` varchar(50) NOT NULL COMMENT '话术 (A：贷前7天的提醒话术 B：贷前3天的话术 C：贷前3天的话术 D：贷前1天的话术 Ps：若话术为空，则使用的是大唐的话术，其余类似due_one之类的均已废弃)',  `call_platform_name` varchar(100) NOT NULL COMMENT '平台名称',  `third_party_system` tinyint(3) unsigned NOT NULL COMMENT '第三方IVR系统，1 = 百可录(暂停使用)，2 = 大唐，3 = 云电帮(暂停使用), 4 = 科大讯飞, 5 = 基立讯，99 = 决策引擎测试',  `send_time` datetime DEFAULT NULL COMMENT '发送时间',  `send_status` tinyint(3) unsigned NOT NULL DEFAULT '0' COMMENT '发送状态，0 = 未发送，1 = 发送成功，2 = 发送失败',  `send_result` tinyint(3) DEFAULT '0' COMMENT 'IVR结果( 0 = 代表无效接听，或者未接听，1 = 有效接听，已通知用户)',  `talking_time` int(10) NOT NULL DEFAULT '0' COMMENT '通话时长',  `task_id` varchar(32) NOT NULL DEFAULT '0' COMMENT '外呼任务ID (只为科大讯飞服务)',  `task_data_id` varchar(32) NOT NULL DEFAULT '0' COMMENT '外呼任务二级ID (只为科大讯飞服务)',  `resend_num` tinyint(3) unsigned NOT NULL DEFAULT '0' COMMENT '重发次数',  `receive_time` datetime DEFAULT NULL COMMENT '接收时间',  `receive_content` text COMMENT '接收内容',  `unique_tab` varchar(100) DEFAULT NULL COMMENT '唯一标识',  `created_at` int(10) unsigned NOT NULL DEFAULT '0' COMMENT '创建时间',  `updated_at` int(10) unsigned NOT NULL DEFAULT '0' COMMENT '更新时间',  PRIMARY KEY (`id`),  KEY `loan_id` (`agentid`,`loan_id`),  KEY `send_result` (`call_mobile`,`send_time`),  KEY `receive_time` (`receive_time`),  KEY `IDX_task_id` (`task_id`),  KEY `IDX_task_data_id` (`task_data_id`)) ENGINE=InnoDB AUTO_INCREMENT=5292233 DEFAULT CHARSET=utf8 COMMENT='催收自动通话表'1 row in set (0.00 sec)

查看warnings

因为这两列为字符串类型 ，但是SQL中并没有加引号！！

`task_id` varchar(32) `task_data_id` varchar(32)

加上引号后查看执行计划

mysql>  explain select task_id FROM mostop_xiaodai_collection_call_auto WHERE task_id = '433423882127424' AND task_data_id =' 27739131157286912';+----+-------------+-------------------------------------+------------+------+------------------------------+------------------+---------+-------+------+----------+-------------+| id | select_type | table                               | partitions | type | possible_keys                | key              | key_len | ref   | rows | filtered | Extra       |+----+-------------+-------------------------------------+------------+------+------------------------------+------------------+---------+-------+------+----------+-------------+|  1 | SIMPLE      | mostop_xiaodai_collection_call_auto | NULL       | ref  | IDX_task_id,IDX_task_data_id | IDX_task_data_id | 98      | const |    1 |     5.00 | Using where |+----+-------------+-------------------------------------+------------+------+------------------------------+------------------+---------+-------+------+----------+-------------+1 row in set, 1 warning (0.00 sec)