使用INSERT发送数据时外键不更新[重复]

Question

This question already has an answer here:

• How to insert values in table with foreign key using MySQL? 3 answers
• Insert into two tables, one having foreign key of the other 1 answer

I'm creating a questionnaire site that asks for the users information and asks questions and sends that data to a database.

What my database looks like:

Customer table

Questions table

Relationship view of Question Table

Me failing to insert my data to the database:

if (isset($_POST['save'])) 
{
    $q1 = $_POST['q1']; 
    $q2 = $_POST['q2'];
    $q3a = $_POST['q3a'];
    $q3b = $_POST['q3b'];
    $q3c = $_POST['q3c'];
    $q3d = $_POST['q3d'];
    $q3e = $_POST['q3e'];
    $q3f = $_POST['q3f'];
    $age = $_POST['age'];
    $gender = $_POST['gender'];
    $work = $_POST ['work'];
    $name = $_POST['name'];
    $contact = $_POST['contact'];

    mysqli_query($conn, "INSERT INTO customer (cust_name, cust_hp, age, sex, work) VALUES ('$name','$contact','$age', '$gender', '$work')");

    mysqli_query($conn, "INSERT INTO question (Q1, Q2, Q3a, Q3b, Q3c, Q3d, Q3e, Q3f) VALUES ('$q1', '$q2', '$q3a', '$q3b', '$q3c', '$q3d', '$q3e', '$q3f')"); 

    header('location: index.php');
}

Current result: everytime I click submit the only the customer details table is updated. If I drop the foreign key restraint and the fk_cust column both tables update without any problem.

My question is how to setup foreign keys so that when I run those two querys my cust_id in customer table and my fk_cust id in the questions table are 'connected'.

Thanks in advanced kind stranger. Apologies if this has been talked to death.

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