Question

I would like to ask something that troubles me many many days…

Here is what I mean:

I create these two tables:

CREATE TABLE IF NOT EXISTS journal (
  issn varchar(20) NOT NULL,
  j_title varchar(100) NOT NULL,
  j_publisher varchar(30) NOT NULL,
  PRIMARY KEY (issn)
) ENGINE=InnoDB;

CREATE TABLE IF NOT EXISTS volume (
  volume_no int(11) NOT NULL,
  issn varchar(20) NOT NULL,
  year int(11) NOT NULL,
  PRIMARY KEY (issn,volume_no),
  FOREIGN KEY (issn) REFERENCES journal(issn)
) ENGINE=InnoDB;

When I try to create this:

CREATE TABLE IF NOT EXISTS issue (
  issue_no int(11) NOT NULL,
  issue_pages varchar(10) NOT NULL,
  issue_date varchar(10) NOT NULL,
  issn varchar(20) NOT NULL,
  volume_no int(11) NOT NULL,
  PRIMARY KEY (issue_no,issn,volume_no),
  FOREIGN KEY (issn) REFERENCES journal(issn),
  FOREIGN KEY (volume_no) REFERENCES volume(volume_no)
) ENGINE=InnoDB;

it throws an error (errno 150)

The error is in the foreign key volume_no.

Without FOREIGN KEY (volume_no) REFERENCES volume(volume_no)

the table is created without a problem…. I can’t explain what’s going on… I have seen it many times again and again but nothing!! Does anybody know what’s going on?

Thanks in advance!!

Answer 1

I could see that the foreign key doesnt include issn but which is actually included in primary key for volumn table.

CREATE TABLE IF NOT EXISTS issue (   issue_no int(11) NOT NULL,  
                                  issue_pages varchar(10) NOT NULL,   
                                  issue_date varchar(10) NOT NULL,  
                                  issn varchar(20) NOT NULL,  
                                  volume_no int(11) NOT NULL,   
                                  PRIMARY KEY (issue_no,issn,volume_no),   
                                  FOREIGN KEY (issn,volume_no) REFERENCES volume(issn,volume_no) ) ENGINE=InnoDB; 

Look at the below sql fiddle.
http://sqlfiddle.com/#!2/55a63