MySQL自用笔记

Posted 2021-06-17 SK特困生

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https://www.bilibili.com/video/BV1UE41147KC?p=4

mysql windows 安装教程

安装官网：mysql.coｍ

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第一课

USE sql_store;#使用这个数据库

#sql中大小写是不区分的，最好用大写

-- select * #选取数据库(*可以返回所有行）

-- from customers

-- where customer_id=1 #如果加上了 -- 这一句就会被省略

-- order by first_name #按照首字母排序

#这些语句都是有顺序的（select-from-where-order by）

select 1, 2; #选取这两个数字

select*from customers;

#对于简单查询来说是可以这样的，但是最好放两行

注意运行完一条需要加；分隔开来

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第二课：select 语句

select first_name,last_name

from customers;

select last_name,first_name,points,points+10 #数字计算式

from customers;

select #可以分行表示！注意运算顺序

    last_name,

    first_name,

    points,

    points*10+100 as "discont factor" #用as取别名,想要插入空格的话，就要用引号

from customers;

select state #distinct 可以移除重复项

from customers;

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第三课：where语句

select*

from customers

where state<>"VA";

# > < >= <= = != <>

#字符串是一串字符序列，需要加引号

 

 select*

from customers

where birth_date>"1990-01-01";

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第四课：and or not

select*

from customers

where birth_date>"1990-01-01" and points >1000;

select*

from customers

where birth_date>"1990-01-01" or points >1000;

select*

from customers

where birth_date>"1990-01-01" or 

(points >1000 and state="va");

#运算顺序：and>or

select*

from customers

where not (birth_date>"1990-01-01" or points >1000);

#上下这两种是一个意思哟！

select*

from customers

where (birth_date<="1990-01-01" and points <= 1000);

#练习题

-- from the order_items table, get the items

-- for order#6

-- where the total price is greater than 30

select *

from order_items

where quantity*unit_price>=30 and order_id=6;

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第五课-in

 

select *

from customers

where state = "va" or state='fl' or state='ga';

#sql中不能连接字符串和布林

select *

from customers

where state not in ('va','fl','ga');

#exercise：return products with

-- quantity in stock equal to 49,38,72

select*

from products

where stock in (49,38,72);

gavin：“为什么最近内容这么干？”

suki：“因为我想水一水”

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