6.MySQL数据库之过滤数据

喜欢ヅ旅行 2023-06-17 14:54 23阅读 0赞

## MySQL数据库之过滤数据 ##

### 1.使用where子句寻找对应数据 ###

数据库：own ->>表：single\_pro

语法：select ...  from  ...  where 过滤条件。

select * from single_pro where counted = 65;

![20191129143443538.png][]

**操作符：**

<table style="width:500px;"> 
 <tbody> 
  <tr> 
   <td style="text-align:center;vertical-align:middle;width:234px;">操作符</td> 
   <td style="text-align:center;vertical-align:middle;width:265px;">说明</td> 
  </tr> 
  <tr> 
   <td style="text-align:center;vertical-align:middle;width:234px;">=</td> 
   <td style="text-align:center;vertical-align:middle;width:265px;">等于</td> 
  </tr> 
  <tr> 
   <td style="text-align:center;vertical-align:middle;width:234px;">&lt;&gt;</td> 
   <td style="text-align:center;vertical-align:middle;width:265px;">不等于</td> 
  </tr> 
  <tr> 
   <td style="text-align:center;vertical-align:middle;width:234px;">!=</td> 
   <td style="text-align:center;vertical-align:middle;width:265px;">不等于</td> 
  </tr> 
  <tr> 
   <td style="text-align:center;vertical-align:middle;width:234px;">&lt;</td> 
   <td style="text-align:center;vertical-align:middle;width:265px;">小于</td> 
  </tr> 
  <tr> 
   <td style="text-align:center;vertical-align:middle;width:234px;">&lt;=</td> 
   <td style="text-align:center;vertical-align:middle;width:265px;">小于等于</td> 
  </tr> 
  <tr> 
   <td style="text-align:center;vertical-align:middle;width:234px;">&gt;</td> 
   <td style="text-align:center;vertical-align:middle;width:265px;">大于</td> 
  </tr> 
  <tr> 
   <td style="text-align:center;vertical-align:middle;width:234px;">&gt;=</td> 
   <td style="text-align:center;vertical-align:middle;width:265px;">大于等于</td> 
  </tr> 
  <tr> 
   <td style="text-align:center;vertical-align:middle;width:234px;">between</td> 
   <td style="text-align:center;vertical-align:middle;width:265px;">在指定的两个值之间</td> 
  </tr> 
 </tbody> 
</table>

### 2.示例：between ###

select * from single_pro where counted between 50 and 100 order by counted desc;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70][]

### 3.空值检查 ###

关键点：使用  is  null 来判断。

检查counted列是否有空值。【一定注意空值不是0】

select * from single_pro where counted is null;

![2019112914471842.png][]

[20191129143443538.png]: https://img-blog.csdnimg.cn/20191129143443538.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20191129144203921.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw==,size_16,color_FFFFFF,t_70
[2019112914471842.png]: https://img-blog.csdnimg.cn/2019112914471842.png