Mysql外鍵約束不正確嗎？

Question

我收到試圖在MySQL中創建一些表與外鍵

CREATE TABLE session (
code CHAR(2) NOT NULL, 
date DATE, 
room VARCHAR(30) NULL, 
CONSTRAINT session_pk PRIMARY KEY (date), 
CONSTRAINT session_fk FOREIGN KEY (code) 
    REFERENCES module(code)); 

CREATE TABLE module (
code CHAR(2) NOT NULL, 
name VARCHAR(30) NOT NULL, 
cost DECIMAL(8,2) NOT NULL, 
credits TINYINT NOT NULL, 
course_code CHAR(3) NOT NULL, 
CONSTRAINT module_pk PRIMARY KEY (code)); 

這裏的時候，錯誤是兩個表我想創建，語法我用火柴W3學校和兩種數據類型都是一樣的，所以我看不出這是不正確，任何幫助，將不勝感激謝謝:)

Answer 1

你試圖創建引用表之前創建表的外鍵。

轉乘查詢的順序將工作：

CREATE TABLE module (
`code` CHAR(2) NOT NULL, 
name VARCHAR(30) NOT NULL, 
cost DECIMAL(8,2) NOT NULL, 
credits TINYINT NOT NULL, 
course_code CHAR(3) NOT NULL, 
CONSTRAINT module_pk PRIMARY KEY (`code`)); 

CREATE TABLE `session` (
`code` CHAR(2) NOT NULL, 
`date` DATE, 
room VARCHAR(30) NULL, 
CONSTRAINT session_pk PRIMARY KEY (`date`), 
CONSTRAINT session_fk FOREIGN KEY (`code`) 
REFERENCES module(`code`)); 

Answer 2

試試這個

CREATE TABLE module (
code CHAR(2) NOT NULL, 
name VARCHAR(30) NOT NULL, 
cost DECIMAL(8,2) NOT NULL, 
credits TINYINT NOT NULL, 
course_code CHAR(3) NOT NULL, 
CONSTRAINT module_pk PRIMARY KEY (code)); 

CREATE TABLE session (
code CHAR(2) NOT NULL, 
date DATE, 
room VARCHAR(30) NULL, 
CONSTRAINT session_pk PRIMARY KEY (date), 
CONSTRAINT session_fk FOREIGN KEY (code) 
    REFERENCES module(code));