编辑代码

CREATE DATABASE test;
use test;
CREATE TABLE student (
	id int,
	name varchar(255),
	address varchar(255),
	city varchar(255),
    chengji  varchar(255)
);

CREATE TABLE number (
	id int,
	name varchar(255),
	address varchar(255),
	ad varchar(255)
);

CREATE TABLE guanxi (
	id int,
	name varchar(255),
	idname varchar(255)
);

INSERT INTO student VALUES (1, '刘一', '郑十家隔壁', '河南','80');
INSERT INTO student VALUES (2, '陈二',  '李四家隔壁', '安徽','22');
INSERT INTO student VALUES (3, '张三',  '白娘子家隔壁', '杭州','11');
INSERT INTO student VALUES (4, '李四',  '许仙家隔壁', '杭州','80');
INSERT INTO student VALUES (5, '王五',  '李四家隔壁', '杭州','22');
INSERT INTO student VALUES (6, '赵六',  '赵六家隔壁', '杭州','33');
INSERT INTO student VALUES (7, '孙七',  '张三家隔壁', '杭州','99');
INSERT INTO student VALUES (8, '周八',  '雷峰塔附近', '杭州','22');
INSERT INTO student VALUES (9, '吴九',  '孙七家隔壁', '杭州','66');
INSERT INTO student VALUES (10, '郑十',  '周八家隔壁', '杭州','81');
 


INSERT INTO number VALUES (1, '刘一', '郑十家隔壁', '985985985');
INSERT INTO number VALUES (2, '陈二', '李四家隔壁', '333222111');

INSERT INTO number VALUES (2, 'aaa', '李四家隔壁', '333222111');

INSERT INTO guanxi VALUES (1, '陈二', 'aaa');

-- SELECT  city, avg(chengji) from  student  group by  city
-- SELECT   avg(chengji) from  student  
-- SELECT * from student order by chengji 

-- SELECT * FROM number where name=(SELECT idname from guanxi where name='陈二')

-- SELECT * from student a  left join number b on a.name=b.name
-- SELECT * from student a  right join number b on a.name=b.name
-- SELECT * from student a  inner join  number b on a.name=b.name