三、基础查询——MySQL数据库之计算列(3)

清疚 2023-06-21 08:54 10阅读 0赞

## 三、基础查询——MySQL数据库之计算列(3) ##

### 1.何为计算列 ###

对数据库的原始数据做一些简单计算，从而对数据有一些简单的掌握。

### 2.计算所有水果的总数 ###

select sum(num) from fruit;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70][]

![20191211223226136.png][]

### 3.查看水果的个数 ###

select count(name) from fruit;

![2019121122351451.png][]

### 4.水果价格提升10%之后的价格 ###

select price*1.1 from fruit;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 1][]

#保留小数位数
    select round(price*1.1,2) from fruit;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 2][]

### 5.显示包括价格提升后的所有数据 ###

select *,round(price*1.1,2) from fruit;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 3][]

### 6.将计算列重命名 ###

select round(price*1.1,2) as new_price from fruit;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 4][]

select *,round(price*1.1,2) as new_price from fruit;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 5][]

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[20191211223226136.png]: https://img-blog.csdnimg.cn/20191211223226136.png
[2019121122351451.png]: https://img-blog.csdnimg.cn/2019121122351451.png
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