yu_fu_a_bu的博客

2.操作表3.操作表中的记录准备工作3.1增删改增加修改删除3.2查询简单查询条件查询排序查询聚合函数

数据库的安装与下载自带客户端的登录与退出，当MySQL服务启动完成后，便可以通过客户端来登录MySQL数据库。注意：确认服务是开启的。

聚合函数#聚合函数#1. 常见的几个聚合函数#1.1 AVG / SUM ：只适用于数值类型的字段（或变量）SELECT AVG(salary),SUM(salary)FROM employees;#1.2 MAX / MIN :适用于数值类型、字符串类型、日期时间类型的字段（或变量）SELECT MAX(last_name),MIN(last_name),MAX(hire_date),MIN(hire_date)FROM employees;SELECT MAX(salary),MIN(

多表查询的分类#多表查询/*select ...,...,...FROM ...WHERE ...AND OR NOT ...ORDER BY ....DESC (ASC)LIMIT ..,..;*/DESC departments;DESC employees;DESC locations;#查询员工名为'Abel'的人在哪个城市工作？SELECT * FROM employeesWHERE last_name = 'Abel';SELECT *FROM depart

多表查询#多表查询/*select ...,...,...FROM ...WHERE ...AND OR NOT ...ORDER BY ....DESC (ASC)LIMIT ..,..;*/DESC departments;DESC employees;DESC locations;#查询员工名为'Abel'的人在哪个城市工作？SELECT * FROM employeesWHERE last_name = 'Abel';SELECT *FROM departme

【MYSQL】排序与分页#排序与分页#无排序SELECT *FROM employees;#1.按照salary从高到低的顺序显示员工信息SELECT employee_id,last_name,salaryFROM employeesORDER BY salary DESC;#按照salary从低到高的顺序显示员工信息SELECT employee_id,last_name,salaryFROM employeesORDER BY salary ASC;SELECT employ

#列的别名只能在 ORDER BY 中使用，不能在WHERE中使用。#如下操作报错！SELECT employee_id,salary salFROM employeesWHERE sal>3000;

运行代码错误提示解决办法多加了 “；”