Question

I’ve been reading some questions with the same problem I have but have not found the solution

Database Estructure

CREATE TABLE material (
  cve_mat varchar(12),
  type_mat varchar(20),
  author_mat varchar(40),
  status varchar(2),
  primary key(cve_mat)   
) ENGINE = INNODB;

CREATE TABLE users (
  cve_user varchar(8),
  name_user varchar(25),
  lastn_user varchar(25),
  email_user varchar(25),
  primary key(cve_user)
)ENGINE = INNODB;

CREATE TABLE material_user (
  cve_mat varchar(8),
  cve_user varchar(8),
  start_mat date,
  end_mat date,
  foreign key(cve_mat) references material(cve_mat)
    ON UPDATE CASCADE
    ON DELETE CASCADE,
  foreign key(cve_user) references users(cve_user)
    ON UPDATE CASCADE
    ON DELETE CASCADE
) ENGINE = INNODB;

And when execute these instructions:

......
$query = "INSERT INTO material_user VALUES ('$cvemat','$ncontrol',NOW(),DATE_ADD(current_date, interval '$days' day))";
$result = mysql_query($query) or die(mysql_error());

if ($result) {
$query = "UPDATE material SET status = 'YES' WHERE material.cve_mat = '$cvemat'";
$result = mysql_query($query) or die(mysql_error());

if ($result){
    return true;
} else {
    return false;
}
} else {
return false;
}

And display this error:

Cannot add or update a child row: a foreign key constraint fails (`biblioteca/material_prestamo`, CONSTRAINT `material_prestamo_ibfk_1` FOREIGN KEY (`cve_mat`) REFERENCES `material` (`cve_mat`) ON DELETE CASCADE ON UPDATE CASCADE)

I would greatly appreciate your help!

Answer 1

First, the column types for the foreign key should match the referencing tables:

material_user

cve_mat varchar(8),

material

cve_mat varchar(12),

Those two column types should be equal.

Before your insert statement you can perform some debugging:

SELECT * FROM material WHERE cve_mat='$cvemat'

If all seems okay, you can run this to find out more details:

SHOW INNODB STATUS;