Необходимо управлять количеством запасов на основе продажи продукта с использованием цикла foreach

У меня есть сценарий для продукта Invoice, который сохраняет информацию о проданном продукте, но он не обновляет количество акций при продаже какого-либо продукта. Количество продукта в запасе остается тем же, что и должно уменьшаться.

вот код для сохранения данных счета-фактуры, используемого для каждого цикла:

<?php

    function saveInvoice( array $data){
            if( !empty( $data ) ){ 
                global $con;

                $count = 0;
                if( isset($data['data'] )){
                    foreach ($data['data'] as $value) {
                        if(!empty($value['product_id'] ))$count++;
                    }
                }

                if($count == 0)throw new Exception( "Please add atleast one product to invoice." );

                return [
                        'success' => true,
                        'uuid' => $uuid,
                        'message' => 'Demo Purpose I have disabled invoice save, Please download script and check in your local machine..'
                    ];

                // escape variables for security
                if( !empty( $data)){
                    $client_id = mysqli_real_escape_string( $con, trim( $data['client_id'] ) );
                    $invoice_total = mysqli_real_escape_string( $con, trim( $data['invoice_total'] ) );
                    $invoice_subtotal = mysqli_real_escape_string( $con, trim( $data['invoice_subtotal'] ) );
                    $tax = mysqli_real_escape_string( $con, trim( $data['tax'] ) );
                    $amount_paid = mysqli_real_escape_string( $con, trim( $data['amount_paid'] ) );
                    $amount_due = mysqli_real_escape_string( $con, trim( $data['amount_due'] ) );
                    $notes = mysqli_real_escape_string( $con, trim( $data['notes'] ) );



                    $id = mysqli_real_escape_string( $con, trim( $data['id'] ) );

                    if(empty($id)){
                        $uuid = uniqid();
                        $query = "INSERT INTO invoices (`id`, `client_id`,  `invoice_total`, `invoice_subtotal`, `tax`,
                                `amount_paid`, `amount_due`, `notes`, `created`, `uuid`)
                                VALUES (NULL, '$client_id',  '$invoice_total', '$invoice_subtotal', '$tax', '$amount_paid', '$amount_due', '$notes',
                                CURRENT_TIMESTAMP, '$uuid')";

                    }else{
                        $uuid = $data['uuid'];
                        $query = "UPDATE `invoices` SET `client_id` = '$client_id', `invoice_total` ='$invoice_total',`invoice_subtotal` = '$invoice_subtotal',
                                `tax` = '$tax', `amount_paid` = '$amount_paid', `amount_due` = '$amount_due', `notes` = '$notes', `updated` = CURRENT_TIMESTAMP
                                WHERE `id` = $id";
                    }
                    if(!mysqli_query($con, $query)){
                        throw new Exception(  mysqli_error($con) );
                    }else{
                        if(empty($id))$id = mysqli_insert_id($con);
                    }

                    if( isset( $data['data']) && !empty( $data['data'] )){
                        saveInvoiceDetail( $data['data'], $id );
                    }
                    return [
                        'success' => true,
                        'uuid' => $uuid,
                        'message' => 'Invoice Saved Successfully.'
                    ];
                }else{
                    throw new Exception( "Please check, some of the required fileds missing" );
                }
            } else{
                throw new Exception( "Please check, some of the required fileds missing" );
            }
        }


    function saveInvoiceDetail(array $invoice_details, $invoice_id = ''){ 
        global $con;
        $deleteQuery = "DELETE FROM invoice_details WHERE invoice_id = $invoice_id";
        mysqli_query($con, $deleteQuery);

        foreach ($invoice_details as $invoice_detail){
            $product_id = mysqli_real_escape_string( $con, trim( $invoice_detail['product_id'] ) );
            $productName = mysqli_real_escape_string( $con, trim( $invoice_detail['product_name'] ) );
            $quantity = mysqli_real_escape_string( $con, trim( $invoice_detail['quantity'] ) );
            $price = mysqli_real_escape_string( $con, trim( $invoice_detail['total'] ) );


            $query = "INSERT INTO invoice_details (`id`, `invoice_id`, `product_id`, product_name, `quantity`, `price`)
                    VALUES (NULL, '$invoice_id', '$product_id', '$productName', '$quantity', '$price')";
            mysqli_query($con, $query);
        }

    }

у нас есть таблица продуктов с is, productname, quantityInStockrow. этот скрипт сохраняет данные о продукте в Invoice_detailsтаблице:

function saveInvoiceDetail(array $invoice_details, $invoice_id = ''){ 
    global $con;
    $deleteQuery = "DELETE FROM invoice_details WHERE invoice_id = $invoice_id";
    mysqli_query($con, $deleteQuery);

    foreach ($invoice_details as $invoice_detail){
        $product_id = mysqli_real_escape_string( $con, trim( $invoice_detail['product_id'] ) );
        $productName = mysqli_real_escape_string( $con, trim( $invoice_detail['product_name'] ) );
        $quantity = mysqli_real_escape_string( $con, trim( $invoice_detail['quantity'] ) );
        $price = mysqli_real_escape_string( $con, trim( $invoice_detail['total'] ) );


        $query = "INSERT INTO invoice_details (`id`, `invoice_id`, `product_id`, product_name, `quantity`, `price`)
                VALUES (NULL, '$invoice_id', '$product_id', '$productName', '$quantity', '$price')";
        mysqli_query($con, $query);
    }

EDIT: найденное решение: $ query2 = "update products set quantityInStock= quantityInStock - '". $ Invoice_detail ["quantity"]. "' Где id = '". $ Invoice_detail [' product_id ']. "'"; mysqli_query ($ con, $ query2);