表结构如下
desc info;
+-------+-----------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------+------+-----+---------+----------------+
| id | int(8) unsigned | NO | PRI | NULL | auto_increment |
| name | varchar(20) | YES | | NULL | |
+-------+-----------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
执行sql.
insert into info values ('', 'xxx');
insert into info values ('', 'yyy');
查询记录.
select * from info;
+----+------+
| id | name |
+----+------+
| 1 | xxx |
| 2 | yyy |
+----+------+
2 rows in set (0.00 sec)
执行下面sql.
select * from info where id = 1;
select * from info where id = '1aaaa';
你先想想结果会是什么。
select * from info where id = 1;
+----+------+
| id | name |
+----+------+
| 1 | xxx |
+----+------+
1 row in set (0.00 sec)
select * from info where id = '1aaaa';
+----+------+
| id | name |
+----+------+
| 1 | xxx |
+----+------+
1 row in set, 1 warning (0.01 sec)
两个sql都查到了id = 1的记录，唯一的区别在于第二个sql有一个warning错误。
show warnings;
+---------+------+-------------------------------------------+
| Level | Code | Message |
+---------+------+-------------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: '1aaaa' |
+---------+------+-------------------------------------------+
1 row in set (0.00 sec)
mysql在查询时，会根据字段类型进行转换，这里1aaaa被转为了1。