MySQL错误：无法添加外键约束？(MySQL error: Cannot add foreign

有永远是错误：“无法添加外键约束”当我创建我的最后一个表 。

操作系统：Mac OS X 10.9
DB：MySQL的5.6.14
DBM：续集专业

CREATE TABLE users (
uid INT AUTO_INCREMENT PRIMARY KEY,
uname VARCHAR(20) NOT NULL,
uemail VARCHAR(20) NOT NULL,
ucity VARCHAR(20),
upassw VARCHAR(20) NOT NULL
);

CREATE TABLE songs(
sid INT AUTO_INCREMENT PRIMARY KEY,
sname VARCHAR(20) NOT NULL,
srldate DATE NOT NULL
);



CREATE TABLE albums (
albid INT AUTO_INCREMENT PRIMARY KEY,
albname VARCHAR(20) NOT NULL,
albrldate DATE NOT NULL,
albrltime TIME NOT NULL
);

CREATE TABLE artists (
aid INT AUTO_INCREMENT PRIMARY KEY,
aname VARCHAR(20) NOT NULL
);

CREATE TABLE genres (
gid INT AUTO_INCREMENT PRIMARY KEY,
gname VARCHAR(20) NOT NULL
);

CREATE TABLE playlists (
uid INT NOT NULL,
sid INT NOT NULL,
plname VARCHAR(20) NOT NULL,
plmdate DATE NOT NULL,
plmtime TIME NOT NULL,
PRIMARY KEY(uid, sid, plname, plmdate, plmtime),
FOREIGN KEY(uid) REFERENCES users(uid),
FOREIGN KEY(sid) REFERENCES songs(sid)
);

CREATE TABLE u_like_a (
aid INT NOT NULL,
uid INT NOT NULL,
PRIMARY KEY(aid, uid),
FOREIGN KEY(aid) REFERENCES artists(aid),
FOREIGN KEY(uid) REFERENCES users(uid)
);

CREATE TABLE be_fan (
aid INT NOT NULL,
uid INT NOT NULL,
PRIMARY KEY(aid, uid),
FOREIGN KEY(aid) REFERENCES artists(aid),
FOREIGN KEY(uid) REFERENCES users(uid)
);

CREATE TABLE follow (
uid INT NOT NULL,
to_uid INT NOT NULL,
PRIMARY KEY(uid, to_uid),
FOREIGN KEY(uid) REFERENCES users(uid),
FOREIGN KEY(to_uid) REFERENCES users(uid)
);

CREATE TABLE u_like_g (
gid INT NOT NULL,
uid INT NOT NULL,
PRIMARY KEY(gid, uid),
FOREIGN KEY(gid) REFERENCES genres(gid),
FOREIGN KEY(uid) REFERENCES users(uid)
);

CREATE TABLE u_share_pl(
uid INT NOT NULL,
from_uid INT NOT NULL,
plname VARCHAR(20) NOT NULL,
plmdate DATE NOT NULL,
plmtime TIME NOT NULL,
PRIMARY KEY(uid, from_uid, plname, plmdate, plmtime),
FOREIGN KEY(uid) REFERENCES users(uid),
FOREIGN KEY(from_uid) REFERENCES users(uid),
FOREIGN KEY(plname) REFERENCES playlists(plname),
FOREIGN KEY(plmdate) REFERENCES playlists(plmdate),
FOREIGN KEY(plmtime) REFERENCES playlists(plmtime)
); #####--->  This is the last table.

错误来自这里。我真的不知道为什么。我有检查类型的所有属性。属性的类型和名称都没有问题。但MySQL的总是说“不能添加外键约束”

这里是你引用错forgien REFERENCES users(from_uid)在上表中。

FOREIGN KEY(from_uid) REFERENCES users(from_uid)

from_uid不属于users

这应该是

FOREIGN KEY(from_uid) REFERENCES users(uid)

您的playLists table有四列的主键的组合，所以你应该提供所有这四个列在forieng关键u_share_pl table 。

另一个复合键作为参考应该是这样一个约束

FOREIGN KEY(from_uid,sid,plname,plmdate,plmtime) REFERENCES playlists(uid,sid,plname,plmdate,plmtime)

你的最后一个表格创建应该是：

CREATE TABLE u_share_pl(
uid INT NOT NULL,
from_uid INT NOT NULL,
sid INT NOT NULL,
plname VARCHAR(20) NOT NULL,
plmdate DATE NOT NULL,
plmtime TIME NOT NULL,
PRIMARY KEY(uid, from_uid, plname, plmdate, plmtime),
FOREIGN KEY(uid) REFERENCES users(uid),
FOREIGN KEY(from_uid,sid,plname,plmdate,plmtime) REFERENCES playlists(uid,sid,plname,plmdate,plmtime)
);