在數據創建表時，遇到ERROR 1215 (HY000): Cannot add foreign key constraint 問題

數據庫已存在表classroom（building,room_no,capacity）,

情況一：

在創建表section;

1. create table section
2. (course_id varchar(20),
3. sec_id varchar(20),
4. semester varchar(20),
5. year varchar(20),
6. building varchar(20),
7. room_no varchar(20),
8. time_slot_id varchar(20),
9. primary key (course_id,sec_id,semester,year),
10. foreign key (building,room_no) references classroom
11. );

 

就出現ERROR 1215 (HY000): Cannot add foreign key constraint  的錯誤；

原因很簡單，設置外鍵的語法應該是這樣的  foreign key (a,b,...) references table_name(a,b,...)

只需將以上語句（ foreign key (building,room_no) references classroom）改成 foreign key (building,room_no) references classroom（building,room_no）這樣既可！！

 

情況二：同樣是錯誤：ERROR 1215 (HY000): Cannot add foreign key constraint問題；

已存在表classroom（building,room_no,capacity）的主鍵是由building，room_no組成，

如果另外一張表A外聯表classroom，外鍵的設置不能單獨的building或room_no，只能設置為classroom和room_no