Question

附件是我尝试为以下实体关系图创建数据库。但我不断收到以下错误：

“SQL0538N FOREIGN KEY”ADVISOR_STUDENT“不符合表或昵称“KISHANPA.STUDENT”的父键的描述。 SQLSTATE = 42830"

对于这4个表：advisor，prereq，teaches，takes。其余的表似乎工作正常。如果有人能指导我正确的方向，我将不胜感激。感谢

create table department (
  dept_name varchar(30) not null, 
  building varchar(30), 
  budget numeric(7,2), 
  constraint department_key primary key (dept_name)
);

create table instructor (
  iid char(9) not null, 
  name varchar(30) not null, 
  dept_name varchar(30) not null, 
  salary numeric(6,2), 
  constraint instructor_key primary key (iid, dept_name), 
  constraint instructor_dept foreign key(dept_name) 
      references department on delete no action
);

create table student (
  sid char(9) not null, 
  name varchar(30) not null, 
  tot_cred smallint, 
  dept_name varchar(30) not null, 
  constraint student_key primary key (sid, dept_name), 
  constraint student_dept foreign key(dept_name) 
      references department on delete no action
);

create table course (
  course_id char(8) not null, 
  title varchar(30) not null, 
  dept_name varchar(30) not null,  
  credits int not null,  
  constraint course_key primary key (course_id, dept_name),  
  constraint course_dept foreign key(dept_name) 
      references department on delete no action
);

create table advisor ( 
  sid char(9) not null,  
  iid char(9) not null,  
  constraint advisor_key primary key (sid, iid),  
  constraint advisor_student foreign key(sid)  
      references student on delete no action,  
  constraint advisor_instructor foreign key (iid)  
      references instructor on delete no action
);

create table prereq ( 
  course_id char(8) not null,  
  prereq_id char(8),  
  constraint prereq_key primary key (course_id),  
  constraint prereq_course foreign key(course_id)  
      references course on delete no action,  
  constraint prereq_precourse foreign key(prereq_id)  
      references course on delete no action
);

create table classroom ( 
  building varchar(30) not null,  
  room_number varchar(10) not null,  
  capicity integer,  
  constraint classroom_key primary key (building, room_number) 
);

create table time_slot ( 
  time_slot_id varchar(10) not null,  
  day varchar(10) not null,  
  start_time time not null,  
  end_time time,  
  constraint time_slot_key primary key (time_slot_id, day, start_time) 
);

create table section ( 
  course_id char(8) not null,  
  sec_id varchar(10) not null,  
  semester char(1) not null,  
  year numeric (4,0) not null,  
  building varchar(30) not null,  
  room_number varchar(10) not null,  
  time_slot_id varchar(10) not null,  
  constraint section_key primary key(course_id, sec_id, year,  
      building, room_number, time_slot_id),  
  constraint section_classroom foreign key(building, room_number)  
      references classroom on delete no action 
);

create table teaches ( 
  iid char(9) not null,  
  course_id char(8) not null,  
  sec_id varchar(10) not null,  
  semester char(1) not null,  
  year numeric(4,0) not null,  
  constraint teaches_key primary key (iid, course_id, sec_id,  
      semester, year),  
  constraint section_instrictor foreign key(iid)  
      references instructor on delete no action,  
  constraint teaches_section foreign key(course_id, sec_id, semester, year) 
      references section on delete no action 
); 

create table takes ( 
  sid char(9) not null,  
  course_id char(8) not null,  
  sec_id varchar(10) not null,  
  semester char(1) not null,  
  year numeric(4,0) not null,  
  grade real,  
  constraint takes_key primary key (sid, course_id, sec_id,  
      semester, year),  
  constraint student_takes foreign key(sid)  
      references student on delete cascade,  
  constraint takes_section foreign key(course_id, sec_id,  
      semester, year) references section on delete cascade 
);

Answer 1

docs这样说：

外键引用相同或中的主键或唯一键另一张桌子。外键分配表示引用根据指定的参考保持完整性约束

您的“advisor_student”引用“sid”，但这不是主键。您需要包括部门或更改设计。

Answer 2

你的问题在于学生的关键。您必须使用相同的列才能加入FK标签。像这样修改你的表学生：

create table student (sid char(9) not null, name varchar(30) not null, tot_cred smallint, dept_name varchar(30) not null, constraint student_key primary key (sid), constraint student_dept foreign key(dept_name) references department on delete no action);

Answer 3

您的主键与多个表的架构图不匹配。

Instructor，student和course在您的DDL中的主键中都有dept_name，但根据Schema图和逻辑上，此字段不应该是任何这些表的主键的一部分。此外，section的主键与Schema图不匹配。它应该是(course_id, sec_id, semester, year)你有很多额外的字段。这将导致teaches和takes上的外键约束出现问题。

最后，模式和DDL中的time_slot文件都有我可以称之为有问题的文件，没有其他输入，主键。我应该只考虑time_slot_id，那么您也可以构建从section到time_slot的外键。

如何在sql中编码这些关系而不会出现错误

3 个答案: