Question

The code below, when executed produces the following error:

Fatal error: Uncaught exception ‘PDOException’ with message ‘SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails

$db->executeUpdate('CREATE TABLE submission_statuses (name VARCHAR(255) NOT NULL, 
                    weight INT NOT NULL, PRIMARY KEY(name)) ENGINE = InnoDB');
$db->executeUpdate('ALTER TABLE submissions ADD CONSTRAINT IDX_4 
                    FOREIGN KEY (status) REFERENCES submission_statuses(name)');
$db->executeUpdate('CREATE INDEX IDX_4 ON submissions (status)');

The tables both use the InnoDB engine.

Answer 1

The table submissions contains a value in the status column that does not exist in the newly created submission_statuses table. The submission_statuses table must be populated before the constraint is created.