MySql constraint violation. Inserting - php

Question

I have database with 5 tables
students PK : ID -> anum, first, last
studentinfo PK/FK : ID -> why, student_commenets, finished, aidyear
Times PK/FK : ID -> signintime, counselor_start_time,
additional_time, finish_time
counselor PK/FK : ID -> firstcounselor, secondcounselor, thirdcounselor
Comments PK/FK : ID -> counselorcomments, additional_commenets
I have a page called signinpage.php
on that page I have to write to three different tables (student, studentinfo, and time)
My code is as fallows :
if (empty($errors) === true)
{
include('core/queries/inserts.updates.selects/students.php');
include('core/queries/inserts.updates.selects/studentinfo.php');
include('core/queries/inserts.updates.selects/signintime.php');
$dbh = null;
header('location: signedin.php');
exit();
}
each of the files are actual insert queries. (if you yall need to see them I will update this post)
The error I am having is :
SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or
update a child row: a foreign key constraint fails (test.times,
CONSTRAINT times_ibfk_2 FOREIGN KEY (id) REFERENCES students
(id) ON DELETE CASCADE ON UPDATE CASCADE)
To add on to this, the first query (the students.php and the second query studentinfo.php)
are inserting just fine. Same ID, the problem occurs with the signintime inserting into table : times.
In phpmyadmin both tables (studentinfo and times) are configured alike with both have cascade on delete and update to the original table (student) since the student him/her starts the session (which is the PK ID).
How can I solved this error?
Edit :
<?php
require('core/init.php');
try
{
$null = NULL;
$query = $dbh->prepare("INSERT INTO `times` (signintime) VALUES (:signintime)");
$query->bindParam(':signintime' , $null);
$query->execute();
}
catch (PDOException $e)
{
error_log($e->getMessage());
die($e->getMessage());
}
?>

Answer 1

Your table design looks wrong to me. I'm assuming there can be multiple entries in the times table for each row in the students table. In that case, you would need the following columns in times:
id - PK
student_id - FK
signintime
counselor_start_time
additional_time
finish_time
Then each row for a particular student would have the same student_id value, but different id values.

Answer 2

The following statements and example is different from the tables you have mentioned but the thought is still the same.
The reason why the error was generated is because you are trying to insert a value on a child table in which that value is not yet present on the parent table. The child table means that it is dependent on the other table (which is the Parent).
To explain further, consider the following schema,
CREATE TABLE StudentList
(
ID INT PRIMARY KEY,
NAme VARCHAR(50)
);
CREATE TABLE AddressList
(
StudentID INT,
Address VARCHAR(50),
CONSTRAINT tb_fk FOREIGN KEY (StudentID)
REFERENCES StudentList(ID)
);
INSERT INTO StudentList VALUES (1, 'Jon');
INSERT INTO StudentList VALUES (2, 'Skeet');
INSERT INTO AddressList VALUES (1, 'Hello');
INSERT INTO AddressList VALUES (2, 'World');
INSERT INTO AddressList VALUES (1, 'Other Address');
There are two tables: StudentList and AddressList. The table Address is the child table and which is dependent to table StudentList (also called the Parent table). The only values that are allowed to be inserted on column StudentID of table AddressList is only 1 and 2 because those are the only IDs found on table StudentList.
When you try to insert record with ID other than 1 and 2 on table Address, eg
INSERT INTO AddressList VALUES (1, 'Other Address');
it will generate an error telling that:
Cannot add or update a child row: a foreign key constraint fails
(db_2_ec2e8.addresslist, CONSTRAINT tb_fk FOREIGN KEY
(StudentID) REFERENCES studentlist (ID)):
because the value of the column StudentID being inserted on the table is not available on the parent table (StudentList).
So, I hoped that this will help you understand now.
SQLFiddle Demo