Inserting into mysql table using foreign key with PHP - php

Question

Hi I have two tables,
users_table and orders table.
users_id is in both tables
as a primary key in users_table and as foreign key in orders_table(referencing users_id in users_table)
When I try to place an order if it's the first time the user is able to place an order but if a user already placed an order the data is not saved to the database in the second attempt.. any Idea why? or any solutions?
I apologise for the bad english
MY PHP CODE:
$query = "INSERT INTO orders_table(users_id, orders_postDate, orders_category, orders_categoryId, orders_name, orders_description, orders_deliveryDate) VALUES('$users_id', '$orders_postDate', '$orders_category', '$orders_categoryId', '$orders_name', '$orders_description', '$orders_deliveryDate')";
$result = mysqli_query($connection, $query);
if($result){
echo "SUCCESS";
}else{
echo "fail";
}
so Let's say that I created an account, signed in and placed an order, the data is successfully on the database. if I try to place a new order with the same user I get the fail message.. so for some reason
mysqli_query($connection, $query);
fails the second time, I am assuming that it is because my foreign key is a primary key? how can I fix this?

Answer 1

Without code/error message it is difficult to say what the issue is. However, you mentioned that user_id is the foreign key for the orders_table, but if it is also used for the primary key for your orders_table it would cause duplication when creating any subsequent orders, hence, insertion of a new order would fail.
These might help you to help us to get a better understanding of whats going on.
How is your orders_table created?
What is the primary key for Orders_table?
How do you assign the primary key (if you do) upon insertion of a new record?
Since you are able to insert the first record that means you get a successful connection. So instead of echoing "success" and "fail", extract the mysqli error instead.
Also, since you are dealing with MySQL and PHP you might want to take a look into using PDO objects instead, if you haven't already. Being able to use prepared statements is a huge plus.

Answer 2

Yes, you are right, if orders_table.user_id with primary key, also there is a 'unique' key. If so, MySql did not allow to paste the same user_id.
Use ALTER TABLE sql command to remove the primary key on orders_table.user_id add add a new column with primary key.
There is code you need:
ALTER TABLE orders_table DROP PRIMARY KEY;
ALTER TABLE orders_table ADD COLUMN `id` int(11) NOT NULL AUTO_INCREMENT;
ALTER TABLE orders_table ADD PRIMARY KEY(`id`);

Answer 3

Your insert query is not getting data from the users_table and so will not be able to insert the right user data into the Orders_table; and second, the order_table is created having user_id as a primary key and foreign key which will cause data duplication. Try altering the table to drop the primary and create another column for it(Primary key).
An example
ALTER TABLE orders_table DROP PRIMARY KEY;
ALTER TABLE orders_table ADD COLUMN 'id' int NOT NULL AUTO_INCREMENT PRIMARY KEY;
That should make your code work now.