Mysql 条件等号的异常

1. 字符型和数字型 MySQL的等号同PHP一样，对等号两端不同的数据类型都有强制类型转换

   mysql> select * from login_log where '1' = 1;
   +----+-----+------+------------+---------------------+-----------+
   | id | uid | fr   | login_date | login_time          | login_ip  |
   +----+-----+------+------------+---------------------+-----------+
   | 27 |   1 | html | 2015-05-29 | 2015-05-29 11:34:36 | 127.0.0.1 |
   | 26 |   1 | html | 2015-05-28 | 2015-05-28 08:35:29 | 127.0.0.1 |
   +----+-----+------+------------+---------------------+-----------+
   2 rows in set (0.00 sec)
   
   mysql> select * from login_log where '1d' = 1;
   +----+-----+------+------------+---------------------+-----------+
   | id | uid | fr   | login_date | login_time          | login_ip  |
   +----+-----+------+------------+---------------------+-----------+
   | 27 |   1 | html | 2015-05-29 | 2015-05-29 11:34:36 | 127.0.0.1 |
   | 26 |   1 | html | 2015-05-28 | 2015-05-28 08:35:29 | 127.0.0.1 |
   +----+-----+------+------------+---------------------+-----------+
   2 rows in set, 1 warning (0.00 sec)
   
   

mysql> select * from login_log where 0.999999999999999999999999999999=1;
Empty set (0.00 sec)

mysql>
```

1. 尾空格 MySQL等号对字符串尾部的空格做忽视的处理

   mysql> select * from login_log where fr="html    ";
   +----+-----+------+------------+---------------------+-----------+
   | id | uid | fr   | login_date | login_time          | login_ip  |
   +----+-----+------+------------+---------------------+-----------+
   | 27 |   1 | html | 2015-05-29 | 2015-05-29 11:34:36 | 127.0.0.1 |
   | 26 |   1 | html | 2015-05-28 | 2015-05-28 08:35:29 | 127.0.0.1 |
   +----+-----+------+------------+---------------------+-----------+
   2 rows in set (0.00 sec)

2. unicode字符集 MySQL的等号认为某些相似字符也是相等的

   mysql> select * from login_log where fr='ħtml';
   Empty set (0.00 sec)
   
   mysql> select * from login_log where fr='ĥtml';
   +----+-----+------+------------+---------------------+-----------+
   | id | uid | fr   | login_date | login_time          | login_ip  |
   +----+-----+------+------------+---------------------+-----------+
   | 27 |   1 | html | 2015-05-29 | 2015-05-29 11:34:36 | 127.0.0.1 |
   | 26 |   1 | html | 2015-05-28 | 2015-05-28 08:35:29 | 127.0.0.1 |
   +----+-----+------+------------+---------------------+-----------+
   2 rows in set (0.00 sec)
   
   mysql>

3. 新型万能密码

   mysql> select * from login_log where fr='abc'='';
   +----+-----+------+------------+---------------------+-----------+
   | id | uid | fr   | login_date | login_time          | login_ip  |
   +----+-----+------+------------+---------------------+-----------+
   | 27 |   1 | html | 2015-05-29 | 2015-05-29 11:34:36 | 127.0.0.1 |
   | 26 |   1 | html | 2015-05-28 | 2015-05-28 08:35:29 | 127.0.0.1 |
   +----+-----+------+------------+---------------------+-----------+
   2 rows in set (0.00 sec)
   
   mysql>

本文为验证. 原文地址: http://www.wupco.cn/?p=93