剑谱第三页，女人真烦人 mysql增删改查，内左右连接 复习笔记

Posted 2021-08-09 两掺豆腐脑丶

创建了两个案例数据库分别为 MyBingSchool、employee_tbl
逻辑很清晰，SQL使用简单。多多复习
– 创建MyBingSchool 设置字符集为utf8(万国码)

create database MyBingSchool CHARSET=utf8;

– 进入数据库

use MyBingSchool;

– 删除表（结构和数据）

drop table Student;

– 学生信息表

create table Student(
-- 主键 学生编号  varchar不能使用default
s_id varchar(20)   COMMENT '学生编号',
s_name varchar(20) UNIQUE  NOT NULL  COMMENT '学生姓名' ,
s_sex varchar(10)   NOT NULL  COMMENT '学生性别' ,
s_brith varchar(20)   NOT NULL  COMMENT '学生出生年月' ,
primary key(s_id)
)ENGINE=InnoDB DEFAULT CHARACTER  SET=utf8;

– 查询表数据

SELECT * FROM Student;
select * from Cuosre;
select * from Sorce;
select * from Teacher;

– 向Student表插入数据

insert into Student VALUES('01','张三','男','1996-01-24');
insert into Student VALUES('02','王二','男','1998-09-01');
insert into Student VALUES('03','李四','男','1978-03-13');
insert into Student VALUES('04','赵雷','男','1996-04-24');
insert into Student VALUES('06','雷子','女','2000-04-24');
insert into Student VALUES(DEFAULT,'小花','女','1996-05-24');

– VARCHAR 插入时也不能使用default
– 修改插入数据

UPDATE  Student set s_id='05' where s_name='小花';

– 删除编号为06的数据

DELETE  from Student WHERE s_id='06';

– 课程表

drop table Cuosre;
create table Cuosre(
c_id VARCHAR(20) COMMENT '课程编号',
c_name varchar(20) UNIQUE NOT NULL  COMMENT '课程名',
t_id varchar(20) NOT NULL COMMENT '教师表id外键',
PRIMARY key (c_id),
CONSTRAINT fk_Cuosre_Teacher foreign  key (t_id) references Teacher(t_id) 
)ENGINE=InnoDB DEFAULT CHARACTER  SET=utf8;

select * from Cuosre;
select * from Sorce;
select * from Teacher;

insert into Cuosre VALUES('01','高数一','01');
insert into Cuosre VALUES('02','英语','02');
insert into Cuosre VALUES('03','政治','03');

– 教师表

drop table Teacher;
create table Teacher(
t_id VARCHAR(20) primary key comment '教师编号',
t_name VARCHAR(20) UNIQUE not null comment '教师名'
)ENGINE=InnoDB DEFAULT CHARACTER  SET=utf8;

select * from Sorce;
select * from Teacher;

insert into Teacher VALUES('01','孙风');
insert into Teacher VALUES('02','李云');
insert into Teacher VALUES('03','周梅');
insert into Teacher VALUES('04','吴兰');

– 成绩表

drop table Sorce;
create table Sorce(
s_id VARCHAR(20) comment '成绩表编号',
c_id VARCHAR(20) comment '外键、课程表编号',
-- 组合主键
s_sroce int(3),
-- 设置组合主键
primary key (s_id,c_id), 
-- 单外键 注意指定于指定的表对应
CONSTRAINT fk_Sorce_Cuosre foreign  key (c_id) references Cuosre(c_id) 
)ENGINE=InnoDB DEFAULT CHARACTER  SET=utf8;

select * from Sorce;

insert into Sorce VALUES('01','01','99');
insert into Sorce VALUES('01','02','89');
insert into Sorce VALUES('01','03','99');

insert into Sorce VALUES('02','01','89');
insert into Sorce VALUES('02','02','60');
insert into Sorce VALUES('02','03','50');

insert into Sorce VALUES('03','01','100');
insert into Sorce VALUES('03','02','90');
insert into Sorce VALUES('03','03','70');

insert into Sorce VALUES('04','01','79');
insert into Sorce VALUES('04','02','80');
insert into Sorce VALUES('04','03','50');

– GROUP BY学习表数据

SET NAMES utf8;
SET FOREIGN_KEY_CHECKS = 0;


-- ----------------------------
--  Table structure for `employee_tbl`
-- employee_tbl 表的结构
-- ----------------------------
DROP TABLE IF EXISTS `employee_tbl`;
CREATE TABLE `employee_tbl` (
  `id` int(11) NOT NULL,
  `name` char(10) NOT NULL DEFAULT '',
  `date` datetime NOT NULL,
  `singin` tinyint(4) NOT NULL DEFAULT '0' COMMENT '登录次数',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `employee_tbl` 
-- employee_tbl 表的数据记录
-- ----------------------------
BEGIN;
INSERT INTO `employee_tbl` VALUES ('1', '小明', '2016-04-22 15:25:33', '1'), ('2', '小王', '2016-04-20 15:25:47', '3'), ('3', '小丽', '2016-04-19 15:26:02', '2'), ('4', '小王', '2016-04-07 15:26:14', '4'), ('5', '小明', '2016-04-11 15:26:40', '4'), ('6', '小明', '2016-04-04 15:26:54', '2');
COMMIT;

SET FOREIGN_KEY_CHECKS = 1;

set names utf8;
 SELECT * FROM employee_tbl;

– 给字段列起别名 fild1 as ‘’

SELECT name,COUNT(*) as '总数' from employee_tbl GROUP BY name DESC;

– WITH ROLLUP 可以实现在分组统计数据基础上再进行相同的统计（SUM,AVG,COUNT…）。

SELECT name ,sum(singin) as '歌曲' FROM employee_tbl GROUP BY name with ROLLUP;

– coalesce 来设置一个可以取代 NUll 的名称

SELECT coalesce(name,'总数') ,sum(singin) as singin_count FROM employee_tbl GROUP BY name with ROLLUP;

SELECT * FROM Student;
select * from Cuosre;
select * from Sorce;
select * from Teacher;

– INNER JOIN（内连接,或等值连接）：获取两个表中字段匹配关系的记录。等价于where

SELECT c_id as '编号' ,c_name as  '课程名' , t_name as '老师' from Cuosre INNER join Teacher ON Cuosre.t_id=Teacher.t_id;

– INNER JOIN等价于where

SELECT c_id as '编号' ,c_name as  '课程名' , t_name as '老师' from Cuosre , Teacher WHERE Cuosre.t_id=Teacher.t_id;

– LEFT JOIN（左连接）：获取左表所有记录，即使右表没有对应匹配的记录。

SELECT c_id as '编号' ,c_name as  '课程名' , t_name as '老师' from Cuosre LEFT join Teacher ON Cuosre.t_id=Teacher.t_id ;

– RIGHT JOIN（右连接）： 与 LEFT JOIN 相反，用于获取右表所有记录，即使左表没有对应匹配的记录。

SELECT c_id as '编号' ,c_name as  '课程名' , t_name as '老师' from Cuosre RIGHT join Teacher ON Cuosre.t_id=Teacher.t_id;