mysql - 我不知道我的错误在哪里 'incorrect syntax near the keyword CONSTRAINT'

Question

CREATE TABLE ClassRegistration(
StudentID int   NOT NULL,
CourseID int    NOT NULL,

CONSTRAINT PK_ClassRegistration PRIMARY KEY (StudentID, CourseID),
CONSTRAINT FK_ClassRegistration_Students,
FOREIGN KEY(StudentID) REFERENCES Students(ID),
ON DELETE CASCADE ON UPDATE CASCADE,

CONSTRAINT FK_ClassRegistration_Classes,
FOREIGN KEY(CourseID) REFERENCES Course(ClassNumber),
ON DELETE CASCADE ON UPDATE CASCADE
)

我认为这只是逗号放在哪里的问题，但我是自学的，所以很难弄清楚。

Answer 1

约束定义没有“嵌入”逗号:

CREATE TABLE ClassRegistration
(
   StudentID int   NOT NULL,
   CourseID int    NOT NULL,

   CONSTRAINT PK_ClassRegistration PRIMARY KEY (StudentID, CourseID),

   CONSTRAINT FK_ClassRegistration_Students   --- no comma here
   FOREIGN KEY(StudentID) REFERENCES Students(ID) -- no comma here
   ON DELETE CASCADE ON UPDATE CASCADE,

   CONSTRAINT FK_ClassRegistration_Classes -- no comma here
   FOREIGN KEY(CourseID) REFERENCES Course(ClassNumber) -- no comma here
   ON DELETE CASCADE ON UPDATE CASCADE
);

顺便说一句:CONSTRAINT PK_ClassRegistration 部分没用。你不能在 MySQL 中给主键约束一个名字(你可以指定它，但它会被忽略并总是命名为PRIMARY)