创建流程回顾

create database test  charset = utf8 //创建数据库

use test  // 使用数据库

select database(); //展示当前使用数据库

create table class(id int auto_increament,key,name varchar(30),num int); //创建一个class 表

show create table class //展示数据表是怎么创建的

insert into class value(,,,,,,,) //全部插入 按顺序插入值

insert into class (id ,name ) values (),() //插入部分值

update class set name=简单说就是对 where id = 1 更新ID为3的全部修改

select * from classes

select gender ,name from classes

select gender as 性别, name as 名字  from classes

select c.name, c.age from classes as c  //classes 重命名为 c 然后查询 name，age

select distinct gender from classes ;   // distinct去重

1.条件查询

1.1  比较运算符 

           <   >    =    >=    <=   !=

select * from students where age>18

select id, name, gender from students where age=18

1.2     逻辑运算符

           and     or       not

          select * form students where age > 18 and age < 28; // 年纪大于 18 小于28的

          select * form students where age > 18 or gender ="女";

           select * form students where not (age > 18 or gender ="女");

1.3模糊查询 like 

查询姓名中以小开始的名字

select name from students where name like "小%"

查询姓名中有 小 的名字

select name from students where name like "%小%"

查询姓名中2个字的名字

select name from students where name like "__"

查询姓名中3个字的名字

select name from students where name like "___"

查询至少有2个字的名字

select name from students where name like "__%"

1.4正则查询 rlike

查询以 周开始的名字

select name from students where name rlike "^周.*"

查询以 周开始伦结尾的名字

select name from students where name rlike "^周.*伦$"

1.4范围查询 

查询年龄为18、34之间的信息

select name age from students where age=18 or age = 34  // 方式一

select name age  from students where age in (18,34)  

查询年龄不为18、34之间的信息

select name age from students where age != 18 or age != 34  // 方式一

select name age from students where age not in (18,34)

查询在18到34连续范围内的 

select name ,age from students where age between 18 and 34

查询不在18到34连续范围内的 

select name ,age from students where age not between 18 and 34

select name ,age from students where not age between 18 and 34

提示 select name ,age from students where age not（ between 18 and 34） 错误的。因为 not between      and 是一个语法  。。。not 不是取反的意思

空判断 

判断 is null

查询身高为空的信息 

select * from students where height is null

判断 is not null

查询身高不为空的信息 

select * from students where height is not null