mysql - 学习<<数据库系统概念>>6ed出现ERROR 1005 (HY000) : Can't create table,

Question

create table classroom
    (building       varchar(15),
     room_number        varchar(7),
     capacity       numeric(4,0),
     primary key (building, room_number)
    );

create table department
    (dept_name      varchar(20), 
     building       varchar(15), 
     budget             numeric(12,2) check (budget > 0),
     primary key (dept_name)
    );

前两个create语句是对的。但是在

create table course
    (course_id      varchar(8), 
     title          varchar(50), 
     dept_name      varchar(20),
     credits        numeric(2,0) check (credits > 0),
     primary key (course_id),
     foreign key (dept_name) references department
        on delete set null
    );

出现ERROR 1005 (HY000): Can't create table ... 我不知道如何解决它。 显然，它的外键数据类型是一致的。

Answer 1

要获取有关错误的详细信息，请运行 SHOW ENGINE INNODB STATUS\G 并查找 LATEST FOREIGN KEY ERROR。它应该是这样的:

------------------------
LATEST FOREIGN KEY ERROR
------------------------
2013-12-04 09:50:19 139428000 Error in foreign key constraint of table test/course:
foreign key (dept_name) references department
        on delete set null
    ):
Syntax error close to:

        on delete set null
    )

解决方法是指定父表的列名，像这样:

create table course
    (course_id      varchar(8), 
     title          varchar(50), 
     dept_name      varchar(20),
     credits        numeric(2,0) check (credits > 0),
     primary key (course_id),
     foreign key (dept_name) references department (dept_name) 
        on delete set null
    );

附言您应该知道 CREATE TABLE 语句中的 CHECK 约束实际上没有做任何事情。如 the manual 中所述:

The CHECK clause is parsed but ignored by all storage engines.