some problems with in_array function - php

Question

Hi I am trying to use in_array, I think my syntax is correct,
but it says "Wrong datatype for second argument"
My code is
$result = mysqli_query($con, "SELECT * FROM Products WHERE Quantity_On_Hand < Min_Stock");
$filter = mysqli_query($con, "SELECT ProductID FROM Orders");
while($row = mysqli_fetch_array($result))
{
if (in_array($row['ProductID'], $filter))
{
}
}
My idea is to find out if the ProductID from Products Table is in the Order Table.
Could someone helps me, Thanks :-)

Answer 1

$filter isn't an array; it's a mysqli_result object:
$filter = mysqli_query($con, "SELECT ProductID FROM Orders");
I think you want to iterate over that, add each ProductID to a new array, and then pass that array to the in_array function like so:
$filter = mysqli_query($con, "SELECT ProductID FROM Orders");
$product_ids = array();
while ($row = $filter->fetch_assoc())
{
$product_ids[] = $row['ProductID'];
}
$result = mysqli_query($con, "SELECT * FROM Products WHERE Quantity_On_Hand < Min_Stock");
while($row = mysqli_fetch_array($result))
{
if (in_array($row['ProductID'], $product_ids))
{
}
}

Answer 2

Your code is failing because $filter is a MySQLi result resource, not an array. Really, this is better accomplished with a simple inner join between the two tables. If a ProductID does not exist in Orders, the INNER JOIN will exclude it from the result set in the first place.
$sql = "
SELECT Products.*
FROM
Products
INNER JOIN Orders ON Products.ProductID = Orders.ProductID
WHERE Quantity_on_Hand < Min_stock";
$result = mysqli_query($con, $sql);
if ($result) {
$results = array();
while ($row = mysqli_fetch_array($result)) {
$results[] = $row;
}
}
// Now $results is a 2D array of all your Products
If instead you want to retrieve all the Products, and simply have an indication of whether it has an active order, use a LEFT JOIN and test if Orders.ProductID is null in the SELECT list:
$sql = "
SELECT
Products.* ,
/* No orders will print 'no-orders' in a pseudo column called has_orders */
CASE WHEN Orders.ProductID IS NULL THEN 'no-orders' ELSE 'has-orders' AS has_orders
FROM
Products
LEFT JOIN Orders ON Products.ProductID = Orders.ProductID
WHERE Quantity_on_Hand < Min_stock";
$result = mysqli_query($con, $sql);
if ($result) {
$results = array();
while ($row = mysqli_fetch_array($result)) {
$results[] = $row;
}
}
// Now $results is a 2D array of all your Products
// And the column $row['has_orders'] will tell you if it has any...
In this case, you may test in a loop over your rowset whether it has orders:
foreach ($results as $r) {
if ($r['has_orders'] == 'has-orders') {
// this has orders
}
else {
// it doesn't...
}
}