一对多/多对多 SQL [英] One to Many/many to many SQL

问题描述

我正在使用 mysql 并且遇到了一些困惑.我创建了两个表 academy 和 courses.我需要帮助来确定如何构建表字段.例如 one to many 模式.一个学院可以提供多门课程，一门课程可以与许多学院一起提供.下表的结构是否正确?

I am working with mysql and running into a little confusion. I have created two tables academy and courses. I am needing help in determining how to structure the table fields. For example the one to many schema. One academy can offer many courses and a course can be offered with many academies. Is the structure for the tables below correct?

create table academy
(
  academy_id int(11) not null auto_increment,
  course_id int()  NOT NULL ,
  name varchar(25) not null,
  primary key (id),
 );
CREATE TABLE course
(
course_id     int(11) not null auto_increment,
course_name   VARCHAR(50)  NOT NULL ,
primary key (course_id),
foreign key (academy_id) REFERENCES academy (academy_id) on delete cascade
); 

期望结果示例

    id Name                  Course

    1  The Alamo School      125 Intro to Programming 
    2  Bearcat High School   125 Intro to Programming 

推荐答案

您真正需要的是一个用于学院的表、一个用于课程的表以及一个可以存储多对多关系的关系表.我将查询留给您以获取您正在寻找的结果:)

What you really need is a table for the academies, one for the courses and a relationship table where you can store the many-to-many relationships. I leave to you the query to get the result you are looking for :)

CREATE TABLE academy
(
  academy_id int(11) not null auto_increment,
  name varchar(25) not null,
  primary key (id),
 );

CREATE TABLE course
(
course_id     int(11) not null auto_increment,
course_name   VARCHAR(50)  NOT NULL ,
primary key (course_id),
); 

CREATE TABLE accademy_course
(
  academy_id int(11) not null,
  course_id     int(11) not null ,
  primary key (academy_id, course_id),
  foreign key (academy_id) REFERENCES academy (academy_id) on delete cascade,
  foreign key (course_id) REFERENCES course (course_id) on delete cascade
); 

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