一、创建数据库db1

CREATE DATABASE `db1` CHARACTER SET utf8mb4 COLLATE UTF8MB4_UNICODE_CI;

1.创建表 字段—表头 student_no,username,sex

CREATE TABLE db1.studentinfo(
student_no INT,
username VARCHAR(50),
sex char
);

2.新增单条插入

INSERT INTO db1.studentinfo(student_no,username,sex) VALUES(1,'zhangsan','男');

多条插入

INSERT INTO db1.studentinfo(student_no,username,sex) VALUES(2,'lisi','男'),(3,'wangwu','女');

3.删除

DELETE FROM db1.studentinfo WHERE student_no =2

4.更新

UPDATE db1.studentinfo SET username = 'zhangsan' ,sex='女' WHERE student_no =1

5.查询

5.1.查询该表全部信息

SELECT * FROM db1.studentinfo;

5.2.查询该表中username，并且要求名字为zhangsan性别女，还可以用（or）

SELECT username FROM db1.studentinfo WHERE username = 'zhangsan' AND sex ='女';

6.时间函数

SELECT DATE(NOW())

7.字段约束

7.1.字段约束 NOT NULL：不为空，DEFAULT：设置默认值

CREATE TABLE db1.stuinfo2(
    id INT NOT NULL,
    user_name VARCHAR(50),
    class VARCHAR(50) DEFAULT '机器人学院'
);

#测试
INSERT INTO db1.stuinfo2(id,user_name) VALUES(1,'zhangsan');
INSERT INTO db1.stuinfo2(id,user_name,class) VALUES(2,'lisi','计算机');

7.2.字段约束 主键：字段唯一，非空,datetime:时间格式

CREATE TABLE db1.USER(
    id INT PRIMARY KEY,
    user_name VARCHAR(50),
    create_time datetime
);
#测试
INSERT INTO db1.user(id,user_name,create_time) VALUES(1,'zhangsan',NOW());

7.3.字段约束自动增长，主键这列一般设置自动增长

CREATE TABLE db1.user1(
    id INT PRIMARY KEY AUTO_INCREMENT,
    user_name VARCHAR(50),
    create_time datetime
);
#测试
INSERT INTO db1.user1(user_name,create_time) VALUES('zhangsan',NOW()),('lisi',NOW());