MySql中的CASE表达式

Posted on Edited on In

[TOC]

起因

在做CTF的时候，发现一个时间盲注，一时间忘记怎么手工，不能忍，果断搜索了一波。

作用

  1. 盲注
  2. 绕过过滤逗号,的注入点

MySql中的CASE表达式

定义参考

  1. 先附上官方参考：MySQL CASE 表达式参考

  2. CASE表达式的两种写法

    1
    2
    CASE value WHEN [compare_value] THEN result [WHEN [compare_value] THEN result ...] [ELSE result] END
    CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END

举例

  1. 第一种语法
     mysql> select case 1 when 1 then 'one' end;
 +------------------------------+
 | case 1 when 1 then 'one' end |
 +------------------------------+
 | one                          |
 +------------------------------+
 1 row in set (0.04 sec)

 mysql> select case 1 when 1=1 then sleep(5) end;
 +-----------------------------------+
 | case 1 when 1=1 then sleep(5) end |
 +-----------------------------------+
 |                                 0 |
 +-----------------------------------+
 1 row in set (5.00 sec)
 
 mysql> select case 1 when 1=2 then sleep(5) when 1=1 then sleep(2) end;
 +----------------------------------------------------------+
 | case 1 when 1=2 then sleep(5) when 1=1 then sleep(2) end |
 +----------------------------------------------------------+
 |                                                        0 |
 +----------------------------------------------------------+
 1 row in set (2.00 sec)

  1. 第二种用法
    mysql> select case when 1=1 then sleep(2) else sleep(5) end;
+-----------------------------------------------+
| case when 1=1 then sleep(2) else sleep(5) end |
+-----------------------------------------------+
|                                             0 |
+-----------------------------------------------+
1 row in set (2.00 sec)

 mysql> select case when 1=2 then sleep(2) else sleep(5) end;

+———————————————–+
| case when 1=2 then sleep(2) else sleep(5) end |
+———————————————–+
| 0 |
+———————————————–+
1 row in set (5.00 sec)