Question

我不确定为什么SQL不适用于Class表。我知道问题与外键行有关，如果我删除表将创建。我的语法有问题吗？

我收到的错误是：错误代码：1005。无法创建表'university.class'（错误号：150）

CREATE TABLE Faculty (
    facId VARCHAR(6),
    name VARCHAR(20) NOT NULL,
    department VARCHAR(20),
    rank VARCHAR(10),
    CONSTRAINT Faculty_facId_pk PRIMARY KEY (facId));

DROP TABLE Class;

CREATE TABLE Class (
    classNumber VARCHAR(8),
    facId VARCHAR(6) NOT NULL,
    schedule VARCHAR(8),
    room VARCHAR(6),
    CONSTRAINT Class_classNumber_pk PRIMARY KEY (classNumber),
    CONSTRAINT Class_facId_fk FOREIGN KEY (facId) REFERENCES Faculty (facId) ON DELETE SET NULL,
    CONSTRAINT Class_schedule_room_uk UNIQUE (schedule, room));

Answer 1

外键不应为NULL

CREATE TABLE类（

classNumber VARCHAR(8),

facId VARCHAR(6) NOT NULL,

schedule VARCHAR(8),

room VARCHAR(6),

CONSTRAINT Class_classNumber_pk PRIMARY KEY (classNumber),

CONSTRAINT Class_facId_fk FOREIGN KEY (facId) REFERENCES Faculty (facId)  ,

CONSTRAINT Class_schedule_room_uk UNIQUE (schedule, room))

Answer 2

您有ON DELETE SET NULL，但Class.facID不允许空值，因此无法实现。

This works并删除在孤儿列中留下NULL列的父记录。

CREATE TABLE Faculty (
    facId VARCHAR(6),
    name VARCHAR(20) NOT NULL,
    department VARCHAR(20),
    rank VARCHAR(10),
    CONSTRAINT Faculty_facId_pk PRIMARY KEY (facId));



CREATE TABLE Class (
    classNumber VARCHAR(8),
    facId VARCHAR(6) NULL,
    schedule VARCHAR(8),
    room VARCHAR(6),
    CONSTRAINT Class_classNumber_pk PRIMARY KEY (classNumber),
    CONSTRAINT Class_facId_fk FOREIGN KEY (facId) REFERENCES Faculty (facId) ON DELETE set null,
    CONSTRAINT Class_schedule_room_uk UNIQUE (schedule, room));


INSERT INTO Faculty 
VALUES('1','Foo','foo','foo');


INSERT INTO Class 
VALUES('1','1','foo','foo');

DELETE FROM Faculty;

SQL语句不正确创建具有外键的表？

2 个答案: