将我的购物车表加入我的客户表

Question

I want to join my cart table to my customer table, so I can add the product_quantity table to prevent users from inputting higher number than the quantity of the product. For me, this can be a way to make this work. Thanks

This is my add_cart.php

<?php

        include('session.php');
        if(isset($_POST['cart'])){
            $id=$_POST['id'];
            $qty=$_POST['qty'];


            $query=mysqli_query($conn,"select * from cart where productid='$id' and userid='".$_SESSION['id']."'");


            if (mysqli_num_rows($query)>0){
                echo "Product already on your cart!";

    }

            else{
                mysqli_query($conn,"insert into cart (userid, productid, qty) values ('".$_SESSION['id']."', '$id', '$qty')");
            }

        }

    ?>

This is my product table.

PRODUCT TABLE

This is my cart table.

Cart Table

Answer 1

You can try to use INNER JOIN to link two table by productid

select * from cart 
INNER JOIN product ON cart.productid = product.productid
where cart.productid='$id' and userid='".$_SESSION['id']."'