Insert data in current table and update another table MySQL - php

Question

I'm having problem with inserting in purchase table and updating facility table. Let's say, user made a purchase with product_id and product_quantity.
The query is running. But it inserts twice with the same data and not updating facility table.
When user hit submit, I want to insert product_id and product_quantity into purchase table. And updating facility table with product_id and product_quantity that associated with it.
Here is my code
<?php
include 'dbconn.inc.php';
include 'functions.inc.php';
$sql1 = "SELECT * FROM facilities";
$res = $mysqli->query($sql1);
$facilities = array();
while( $row = $res->fetch_array(MYSQLI_ASSOC) ){
$facilities[]['id'] = $facilities_id;
$facilities[]['product_id'] = $facilities_product_id;
$facilities[]['product_current_quantity'] = $product_current_quantity;
}
$id = $mysqli->real_escape_string ($_POST['id']);
$purchase_id = $mysqli->real_escape_string( $_POST['purchase_id'] );
$facility_id = $mysqli->real_escape_string( $_POST['facility_id'] );
$product_quantity = $mysqli->real_escape_string( $_POST['product_quantity'] );
$sql1 = "UPDATE facilities
SET
`product_current_quantity` = '$product_quantity + $product_current_quantity'
WHERE $facility_id = $facilities_id AND $id = $facilities_product_id ";
$sql = "INSERT INTO purchases
(
`purchase_id`,
`facility_id`,
`product_quantity`,,
`product_id`
)
VALUES
(
'$purchase_id',
'$facility_id',
'$product_quantity',
'$id'
)";
I did some research and I think I need to use triggers. But I never work with triggers before. Any helps would be great. Thank you!

Answer 1

Please execute your query and better use echo statement if you have doubt in query.
use "php.net"

Answer 2

used this code to your updates
product_current_quantity = product_current_quantity + $product_current_quantity
how many number they can add to your product Quantity and they sum the current number.

Answer 3

You have used insert query and update query for the same variable $sql without any condition. If so always your following query only executes.
Then anymore no update only insertion will reflect in your table.
$sql = "INSERT INTO purchases
(
`purchase_id`,
`facility_id`,
`product_quantity`,,
`product_id`
)
VALUES
(
'$purchase_id',
'$facility_id',
'$product_quantity',
'$id'
)";