无法弄清楚为什么MySql数据库语法无法编译

Question

我在为自己的个人项目编写的数据库中遇到此语法错误，并且不确定为什么会发生此错误，我们将不胜感激！现在，所需的结果只是编译，而该错误是一个简单的语法错误。

问题表是团队表。

  

错误代码：1215：无法添加外键约束。

-- CREATE DATABASE basketBall;
  DROP TABLE LEAGUE;
 -- DROP TABLE TEAM;
  DROP TABLE SESSION;
CREATE TABLE LEAGUE (
    id INT NOT NULL AUTO_INCREMENT,
    name VARCHAR(100) NOT NULL UNIQUE,
    PRIMARY KEY(id)
);

CREATE TABLE SESSION (
    year INT NOT NULL,
    season VARCHAR(50) NOT NULL,
    division VARCHAR(5) NOT NULL,
    PRIMARY KEY(year, season, division),
    CONSTRAINT chk_season CHECK (season IN ('Fall', 'Winter', 'Spring', 'Summer'))
);

CREATE TABLE TEAM (
    id INT NOT NULL AUTO_INCREMENT,
    name VARCHAR(255) NOT NULL,
    season VARCHAR(50) NOT NULL,
    year INT NOT NULL,
    division VARCHAR(5) NOT NULL,
    PRIMARY KEY(id),
    FOREIGN KEY(season) REFERENCES SESSION(season),
    FOREIGN KEY(year) REFERENCES SESSION(year),
    FOREIGN KEY(division) REFERENCES SESSION(division)   

);

CREATE TABLE PLAYER (
    id INT NOT NULL AUTO_INCREMENT,
    fname VARCHAR(30) NOT NULL,
    lname VARCHAR(30) NOT NULL,
    lid INT,
    PRIMARY KEY(id)
);

CREATE TABLE GAME (
    id INT NOT NULL AUTO_INCREMENT,
    time VARCHAR(5),
    court VARCHAR(20),
    date DATE,
    PRIMARY KEY(id)
);

CREATE TABLE STATS  (
    pid INT NOT NULL,
    gid int NOT NULL,
    pts INT NOT NULL,
    fgm INT NOT NULL,
    fga INT NOT NULL,
    fta INT NOT NULL,
    ftm INT NOT NULL,
    3fgm INT NOT NULL,
    3fga INT NOT NULL,
    oreb INT NOT NULL,
    dreb INT NOT NULL,
    ast INT NOT NULL,
    stl INT NOT NULL,
    blk INT NOT NULL,
    turnover INT NOT NULL,
    eff INT NOT NULL,
    pf INT NOT NULL,
    min INT NOT NULL,
    PRIMARY KEY(pid, gid),
    FOREIGN KEY(pid) REFERENCES PLAYER(id),
    FOREIGN KEY(gid) REFERENCES GAME(id)
);



CREATE TABLE Players_on_Team (
    tid INT NOT NULL,
    pid INT NOT NULL,
    PRIMARY KEY(tid, pid),
    FOREIGN KEY(tid) REFERENCES TEAM(id)

);

CREATE TABLE League_Sessions (
    lid INT NOT NULL,
    year INT NOT NULL,
    season VARCHAR(50) NOT NULL,
    division VARCHAR(5) NOT NULL,
    PRIMARY KEY(lid, year, season, division),
    FOREIGN KEY(lid) REFERENCES LEAGUE(id) 
);

Answer 1

在外键中引用的列必须被索引。 TEAM中的这两个外键：

FOREIGN KEY(season) REFERENCES SESSION(season),
FOREIGN KEY(division) REFERENCES SESSION(division)   

指的是没有索引的列。它们是多列索引的一部分，但是只有多列索引的前缀才是这些特定列上的索引。

您可以在season表的division和SESSION列上添加单独的索引。但是，制作多列外键可能更合适：

FOREIGN KEY (year, season, division) REFERENCES SESSION(year, season, division)

Answer 2

我刚刚尝试过，它执行时没有任何错误。