5.6中使用字符串存放时间，导致隐式转换发生的记录
CREATE TABLE `test_date` (
`id` int(11) DEFAULT NULL,
`gmt_create` varchar(100) DEFAULT NULL,
KEY `ind_gmt_create` (`gmt_create`)
) ENGINE=InnoDB AUTO_INCREMENT=524272;
5.5：
mysql> explain select * from test_date where gmt_create BETWEEN DATE_ADD(NOW(), INTERVAL - 1 MINUTE) AND DATE_ADD(NOW(), INTERVAL 15 MINUTE) ;
+----+-------------+-----------+-------+----------------+----------------+---------+------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------+-------+----------------+----------------+---------+------+------+-------------+
| 1 | SIMPLE | test_date | range | ind_gmt_create | ind_gmt_create | 303 | NULL | 1 | Using where |
5.6:
mysql> explain select * from test_date where gmt_create BETWEEN DATE_ADD(NOW(), INTERVAL - 1 MINUTE) AND DATE_ADD(NOW(), INTERVAL 15 MINUTE) ;
+----+-------------+-----------+------+----------------+------+---------+------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------+------+----------------+------+---------+------+---------+-------------+
| 1 | SIMPLE | test_date | ALL | ind_gmt_create | NULL | NULL | NULL | 2849555 | Using where |
+----+-------------+-----------+------+----------------+------+---------+------+---------+-------------+
| Warning | 1739 | Cannot use range access on index 'ind_gmt_create' due to type or collation conversion on field 'gmt_create'
