MySQL——基础查询【1】

ゝ一纸荒年。 2023-06-18 09:58 37阅读 0赞

## SQL——基础查询 ##

数据库：own  ->>表：student

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70][]

### 1.查看特定的列 ###

语法：select \[列名\] from \[表名\];

**(1)查看单列**

描述：查看student表中的name列。

select name from student;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 1][]

**(2)查看多列**

描述：查看student表中的name,gender,academy列。

select name,gender,academy from student;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 2][]

**(3)查看所有列**

描述：查看student表中的所有列

select * from student;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 3][]

### 2.计算列 ###

数据库：own ->>表：fruits

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 4][]

**(1)统计所有的水果个数**

描述：对表fruits中的num列求和。

select sum(num) from fruits;

![20191201214403282.png][]

**(2)查询fruits表中字段price的个数**

描述：查询fruits表中price的个数。

select count(price) from fruits;

![20191201214622521.png][]

**(3)算数运算符直接作用于某(些)列**

描述：查询friuts表中price价格提高20%之后的结果

select price*1.2 from fruits;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 5][]

**(4)查询水果总金额**

描述：查询fruits表中price\*num的值之后求和

select sum(price*num) as total_price from fruits;

![20191201215118585.png][]

### 3.where子查询 ###

使用关系运算符：>、<、=、>=、<=、!=、<>

**(1)查询所有10元以上的水果**

select * from fruits where price>10;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 6][]

**(2)查询数量小于10个的水果**

select * from fruits where num<10;

![20191201222447615.png][]

使用逻辑运算符：not、and、or

**(3)查找所有数量大于20个的水果**

select * from fruits where not num<20;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 7][]

**(4)查找所有数量大于10个，并且价格高于10元的水果**

select * from fruits where num>10 and price>10;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 8][]

**(5)查找所有数量大于10个或者价格高于10元的水果**

select * from fruits where num>10 or price>10;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 9][]

范围运算符：between...and...、not between ... and ...

**(5)查找价格在10到20之间的水果**

select * from fruits where price between 10 and 20;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 10][]

**(6)查找价格不在10到20之间的水果**

select * from fruits where price not between 10 and 20;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 11][]

列表运算符：in (value1, value2,...)、  not  in(value1, value2,...)

**(7)查找所有价格是1元、8元和12元的水果**

select * from fruits where price in (1,8,12);

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 12][]

**(8)查找所有价格不是1元、8元和12元的水果**

select * from fruits where price not in (1,8,12);

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 13][]

### 4.排序 ###

**(1)根据价格对水果排序【默认升序排列】**

select * from fruits order by price;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 14][]

**(2)根据价格对水果排序【使用降序方式(关键字desc)】**

select * from fruits order by price desc;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 15][]

**(3)检索出所有大于10元的水果，并且对水果降序排列，然后计算出每种水果的金额**

select *,price*num as total_price from fruits where price>10 order by price desc;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 16][]

### 5.limit关键字 ###

**返回指定的前n个记录**

select * from fruits where price>10 limit 5;

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 17][]

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[20191201214403282.png]: https://img-blog.csdnimg.cn/20191201214403282.png
[20191201214622521.png]: https://img-blog.csdnimg.cn/20191201214622521.png
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[20191201215118585.png]: https://img-blog.csdnimg.cn/20191201215118585.png
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