Question

I want to create 2 tables in MySQL where the second table has a foreign key from my base table.

The problem is when I try to create the second table I get errno:150. Which fails because the foreign keys are null.

How can I create the second table properly?

More details

My first table has 5 attributes and the first attribute is the Primary key.

My second table has 3 attributes. The 1st and 2nd attribute of this table reference the first 2 attributes from the first table.

All the variables are varchar and all are same length. Any suggestions?

Answer 1

I think the proper way to fix this, given that we can’t see your code, would be on MySQL – Foreign Key documentation page.

See their example below:

CREATE TABLE parent (id INT NOT NULL,
                     PRIMARY KEY (id)
) ENGINE=INNODB;
CREATE TABLE child (id INT, parent_id INT,
                    INDEX par_ind (parent_id),
                    FOREIGN KEY (parent_id) REFERENCES parent(id)
                      ON DELETE CASCADE
) ENGINE=INNODB;

This line is precisely what you need to do : FOREIGN KEY (parent_id) REFERENCES parent(id).