無法將外鍵添加到mysql數據庫

Question

我試圖構建下面的模式：

！

當我嘗試添加這些外鍵後插入數據到表後，我收到錯誤說：「錯誤1452（23000）：無法添加或更新子行：外鍵約束失敗」：

alter table takes add foreign key (course_id,sec_id,semester,year) references section (course_id,sec_id,semester,year) on update cascade on delete cascade; 

alter table prereq add foreign key (prereq_id) references course (course_id) on update cascade on delete cascade; 

alter table course add foreign key (dept_name) references department (dept_name) on update cascade on delete cascade; 

我不明白爲什麼我可以爲其他領域做，但不是爲了這些。所有表格都啓用了engine = innodb。

有什麼建議嗎？

該表具有以下值：

mysql> select * from prereq;       
+-----------+-----------+ 
| course_id | prereq_id | 
+-----------+-----------+ 
| BIO667 | BIO304 | 
| CIS621 | CIS220 | 
| CIS637 | CIS108 | 
| CIS637 | CIS220 | 
| MAT647 | MAT235 | 
+-----------+-----------+ 

mysql> select * from takes;       
+-----+-----------+--------+----------+------+-------+ 
| ID | course_id | sec_id | semester | year | grade | 
+-----+-----------+--------+----------+------+-------+ 
| 100 | CIS621 | 010 | Fall  | 2012 | B+ | 
| 100 | CIS637 | 010 | Fall  | 2011 | A  | 
| 104 | CIS621 | 010 | Fall  | 2012 | B+ | 
| 104 | CIS637 | 010 | Fall  | 2012 | B- | 
| 206 | BIO667 | 1  | Spring | 2012 | A- | 
| 476 | MAT647 | 010 | Spring | 2011 | B  | 
+-----+-----------+--------+----------+------+-------+ 

mysql> select * from course; 
+-----------+--------------+-----------+---------+ 
| course_id | title  | dept_name | credits | 
+-----------+--------------+-----------+---------+ 
| BIO667 | Gene Theory | BIOTECH |  4 | 
| CIS621 | Algorithms | CIS  |  3 | 
| CIS637 | Database  | CIS  |  3 | 
| MAT647 | Calculus - I | MATH  |  3 | 
+-----------+--------------+-----------+---------+ 


mysql> select * from section; 
+-----------+--------+----------+------+----------+---------+--------------+ 
| course_id | sec_id | semester | year | building | room_no | time_slot_id | 
+-----------+--------+----------+------+----------+---------+--------------+ 
| BIO667 | 1  | Spring | 2012 | Brown |  116 |   2 | 
| CIS621 | 010 | Fall  | 2012 | Gore  |  114 |   1 | 
| CIS637 | 010 | Fall  | 2011 | Smith |  102 |   3 | 
| MAT647 | 010 | Spring | 2011 | Memorial |  126 |   4 | 
+-----------+--------+----------+------+----------+---------+--------------+ 

Answer 1

在表takes此行

| 104 | CIS637 | 010 | Fall  | 2012 | B- | 

沒有匹配其在section所有鍵（2012年丟失）

請檢查所有的鑰匙都要小心。