学习新建查询

1、创建数据表——DDL语句

CREATE TABLE `student` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '学号',
  `createDate` datetime DEFAULT NULL COMMENT '创建时间',
  `userName` varchar(20) DEFAULT NULL COMMENT '姓名',
  `pwd` varchar(36) DEFAULT NULL COMMENT '密码',
  `phone` varchar(11) DEFAULT NULL COMMENT '手机号',
  `age` tinyint(3) unsigned DEFAULT NULL COMMENT '年龄',
  `sex` char(2) DEFAULT NULL COMMENT '性别',
  `introduce` varchar(255) DEFAULT NULL COMMENT '简介',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

2、插入数据——DML语句

insert into student values(0,'2024-02-25 10:10:10','盘古',
'123456','15612345678',255,'神','开天辟地第一人。');
insert into student values(0,'2024-02-25 10:10:10','女娲',
'123456','15612345678',200,'女','多次造人最终成功。');
insert into student values(0,'2024-02-25 10:10:10','伏羲',
'123456','15612345678',215,'神','先天八卦');
insert into student values(0,'2024-02-25 10:10:10','神农',
'123456','15612345678',155,'男','尝百草，死与断肠草下。');
insert into student values(0,'2024-02-25 10:10:10','嫘祖',
'123456','15612345678',115,'神','教会百姓养蚕织布');
insert into student values(0,'2024-02-25 10:10:10','蚩尤',
'123456','15612345678',155,'男','锻造大神，坐下食铁巨兽。');
insert into student (userName,age,introduce) values('仓颉',125,'中国象形文字');

3、基础查询——DQL语句

select userName as '用户名',age 年龄,sex '性 别',introduce '简介' 
from student where pwd is not null;
# 去重查询dis tin ct
select distinct sex '性别类型' from student;
# 排序order by
select * from student order by userName desc;
# 分页查询 -limit·是一个重载的函数，当只有1个参数的时候代表显示行数
# 两个参数limit分页：参数1、从N行开始查询=(当前页-1)*每页条数
select * from student limit 6,3;