multiple foreign keys cannot be added - mysql

Question

I am wondering why i cannot be able to add this foreign keys.This is my schema
CREATE TABLE members(
member_id INT NOT NULL AUTO_INCREMENT,
name VARCHAR(50) NOT NULL,
num_1 int,
num_2 int,
password VARCHAR(50) NOT NULL,
PRIMARY KEY (member_id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE contacts(
contact_id INT NOT NULL AUTO_INCREMENT,
s1 int,
phone_number VARCHAR(10) NOT NULL,
s2 int,
s3 int,
PRIMARY KEY (contact_id),
FOREIGN KEY (s1) REFERENCES members(num_1) ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (s2) REFERENCES members(num_2) ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (s3) REFERENCES members(member_id) ON DELETE CASCADE ON UPDATE CASCADE
)ENGINE=InnoDB DEFAULT CHARSET=utf8
I get this error on the mysql terminal
ERROR 1215 (HY000): Cannot add foreign key constraint
Is there a problem with my schema?.

Answer 1

Works for me this way:
CREATE TABLE members(
member_id INT NOT NULL AUTO_INCREMENT,
name VARCHAR(50) NOT NULL,
num_1 int,
num_2 int,
password VARCHAR(50) NOT NULL,
PRIMARY KEY (member_id),
key idx_num1 (num_1),
key idx_num2 (num_2)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE contacts(
contact_id INT NOT NULL AUTO_INCREMENT,
s1 int,
phone_number VARCHAR(10) NOT NULL,
s2 int,
s3 int,
PRIMARY KEY (contact_id),
FOREIGN KEY (s1) REFERENCES members(num_1) ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (s2) REFERENCES members(num_2) ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (s3) REFERENCES members(member_id) ON DELETE CASCADE ON UPDATE CASCADE
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
Just added
key idx_num1 (num_1),
key idx_num2 (num_2)
in table members. Foreign keys need to reference an indexed column (not necessarily unique and not necessarily NOT NULLable).
From the manual:
InnoDB permits a foreign key to reference any index column or group of columns. However, in the referenced table, there must be an index where the referenced columns are listed as the first columns in the same order.