Question

目前我正在使用。我希望减少关联表。并达到相同的目标。有些人帮我找到解决方案。

 CREATE TABLE sys_student_t (
 student_id MEDIUMINT NOT NULL AUTO_INCREMENT,
 student_name VARCHAR(255),
 PRIMARY KEY (student_id)
);

 CREATE TABLE sys_classrooms_t (
  classroom_id MEDIUMINT NOT NULL AUTO_INCREMENT,
  classroom_name VARCHAR(255),
  PRIMARY KEY (classroom_id)
 );

 CREATE TABLE student_classroom_association_t (
  association_id MEDIUMINT NOT NULL AUTO_INCREMENT,
  classroom_id MEDIUMINT NOT NULL,
  student_id MEDIUMINT NOT NULL,
  FOREIGN KEY (student_id) REFERENCES sys_student_t (student_id),
  FOREIGN KEY (classroom_id) REFERENCES sys_classrooms_t    (classroom_id),
  PRIMARY KEY (association_id)
 );

这是小提琴链接： - http://www.sqlfiddle.com/#!9/ada4fd/2 感谢

Answer 1

“多对多”关系总是需要额外的表格。您唯一能做的就是将关联表的主键更改为student_id和classroom_id对。

CREATE TABLE student_classroom_association_t (
  classroom_id MEDIUMINT NOT NULL,
  student_id MEDIUMINT NOT NULL,
  FOREIGN KEY (student_id) REFERENCES sys_student_t (student_id),
  FOREIGN KEY (classroom_id) REFERENCES sys_classrooms_t    (classroom_id),
  PRIMARY KEY (student_id, classroom_id)
 );

如何关联没有关联表的两个表？

1 个答案: