-- 创建数据库
create database if not exists school default charset=utf8;
-- 使用数据库
use school;
-- 创建表格
creat table studentinfo (
id int primary key auto_increment ,
name varchar(20) ,
sex char ,
age int ,
address varchar(100)
);
-- 查看数据表
show tables;
-- 插入数据
insert into studentinfo (name ,sex,age , address) values ("贾宝玉","男"，18，"北平")，
("贾政", "男", 40 ,"浙江")，("晴雯"，"女"，20,"四川")，("袭人","女",29,"贵州"),
("薛宝钗","女",19,"北平")，("林黛玉"，"女"，19，"浙江")；
-- 查看数据 通配符 * 表示所有
select * from studentinfo;
-- 手动写出字段 全量查询
select id, name ,sex , age ,address from studentinfo;
-- 只查询指定的数据列
select id, name ,sex from studentinfo;
-- 条件查询
selecct * from studentinfo where sex='女';
-- 根据查询结果排序 order by
select * grom studentinfo order by age aesc;
-- 显示查询结果的条数
select * from studentinfo limit 3 ;
-- 复合
select * from studentinfo where sex='女' order by age desc limit 3;
-- 别名 AS as 可以省略
select id as 编号 ,name as 姓名，sex as 性别 ，age as 年龄， address as 地址 from studentinfo；
select id 编号，name 姓名， sex 性别，age 年龄 ，address 地址 studentinfo;
-- 单条件查询
select * from studentinfo where age<20;
select * from studentinfo where age is not null;
-- 多条件查询
-- 不等于
select * from studentinfo where age!=20;
select * from studentinfo where age<>20;
select * from studentinfo where not (age=20);
-- 与 或
select * from studentinfo where age >20 && sex='女';
select * from studentinfo where age >20 and sex='女';
select * from studentinfo where age >20 || sex='女';
select * from studentinfo where age >20 or sex='女';
-- 去重 去除重复的数据
select distinct name,sex,age,address from studentinfo;
