2021-06-04模糊查询与分组查询

create database schooldb default charset=utf8;

use schooldb;

create  table  student(

`name`varchar(10),

sex char,

age int,

address varchar(100)

);

insert into student values("张无忌",'男',18,"光明顶")，("张三丰",'男',50,"武当山")，("花无缺",'男',20,"四川"

)，("张三",'男',29,"四海"),("李丰",'男',29,"蜀国")

;

select * from student;

-- 模糊查询 like  % 表示 0-n个    _表示一个

select * from student;

select * from student  where  `name` like "张%";

select * from student  where  `name` like "张_";

select * from student  where  `name` like "%_丰"

--聚合函数

select avg(age) from student;

select count(*) from student;

select max(age) from student;

select min(age) from student;

select sum(age) from student;

insert into student values("任盈盈",'女',17,"黑木崖")，("东方不败",'女',35,"黑木崖")，("依琳",'女',25,"峨眉");

--分组求平均年龄

select sex , avg(age) from student group by sex;

select sex , avg(age) from student group by sex='女';

select  address , `name` ,sex  ,age from student group by address having sex='男' order by age desc ;

select  address , `name` ,sex  ,age from student  where `name` like "张%"group by address having sex='男' order by age desc ;