尝试定义外键时出现“表中不存在关键列”的错误。

Question

我正在尝试设置一个MySQL脚本来创建5个表。在三个表中，都有一个FOREIGN KEY，但是对于这三个表，都出现了相同的错误：

Error Code: 1072. Key column ... doesn't exist in table

其中...是Gebaeude、Dept_Name和Mat_Nr

这是脚本

use cs261_24;

drop table if exists Professor;
drop table if exists Departement;
drop table if exists Gebaeude;
drop table if exists Student;
drop table if exists Pruefung;


CREATE TABLE Gebaeude (
                        Gebaeude    VARCHAR(20) NOT NULL PRIMARY KEY,
                        Hauswart    VARCHAR(20) NOT NULL,
                        Adresse     VARCHAR(20) NOT NULL
)engine = innodb;

CREATE TABLE Professor  (
                        P_ID        INTEGER PRIMARY KEY CHECK (P_ID > 0),
                        P_Name      VARCHAR(20) NOT NULL,
                        Dept_Name   VARCHAR(20) NOT NULL,
                        Raum        INTEGER UNIQUE CHECK (Raum > 0),
                        Tel         INTEGER(10) UNIQUE CHECK (Tel > 210000000),
                        FOREIGN KEY (Gebaeude) REFERENCES Gebaeude (Gebaeude) 
)engine = innodb;

CREATE TABLE Departement (
                        Dept_Name   VARCHAR(20) NOT NULL PRIMARY KEY,
                        Vorsteher   VARCHAR(20) NOT NULL
)engine = innodb;

CREATE TABLE Student (
                        Mat_Nr      INTEGER(8) PRIMARY KEY CHECK (Mat_Nr > 0),
                        S_Name      VARCHAR(20) NOT NULL,
                        Semester    INTEGER CHECK(Semester > 0),
                        FOREIGN KEY (Dept_Name) REFERENCES Departement (Dept_Name) 
)engine = innodb;

CREATE TABLE Pruefung (
                        Pr_ID       INTEGER PRIMARY KEY CHECK(Pr_ID > 0),
                        Fach        VARCHAR(20) NOT NULL,
                        Pruefer     VARCHAR(20) NOT NULL,
                        Note        FLOAT CHECK (Note >= 1 AND Note <= 6),
                        FOREIGN KEY (Mat_Nr) REFERENCES Student (Mat_Nr)
)engine = innodb;

为什么？我使用MySQL Workbench，可以清晰地看到创建的表格，加上特定列被标记为主键！

- Valentino Ru

Answer 1

你做错了，看看这个例子。

http://www.sqlfiddle.com/#!2/a86cf

你的外键行应该更像这样：

FOREIGN KEY (将成为外键的字段) REFERENCES 要引用的表 (引用的字段)

例如=

CREATE TABLE Gebaeude (
                        Gebaeude    VARCHAR(20) NOT NULL PRIMARY KEY,
                        Hauswart    VARCHAR(20) NOT NULL,
                        Adresse     VARCHAR(20) NOT NULL
)engine = innodb;

CREATE TABLE Professor  (
                       Gebaeude_FK varchar(20) NOT NULL,
                        P_ID        INTEGER PRIMARY KEY CHECK (P_ID > 0), 
                        P_Name      VARCHAR(20) NOT NULL,
                        Dept_Name   VARCHAR(20) NOT NULL,
                        Raum        INTEGER UNIQUE CHECK (Raum > 0),
                        Tel         INTEGER(10) UNIQUE CHECK (Tel > 210000000),
                        FOREIGN KEY (Gebaeude_FK) REFERENCES Gebaeude (Gebaeude) 
)engine = innodb;

- jcho360

Answer 2

在将其作为外键约束之前，您必须在每个表中创建列。

请参阅此链接以获取参考资料：链接

- Jordan Kaye