Welke waarde kan ik doorgeven om alles te selecteren?
$cat_id = $_GET['cat_id'];
$sql = "SELECT * FROM producten WHERE producten.cat_id = '$cat_id'";
$result = $conn->query($sql);
$cat_id = $_GET['cat_id'];
$sql = "SELECT * FROM producten WHERE producten.cat_id = '$cat_id'";
$result = $conn->query($sql);
<?php
$sql = 'SELECT * FROM producten';
if (isset($_GET['cat_id']) && ctype_digit($_GET['cat_id'])) {
$sql .= ' WHERE cat_id = ' . $_GET['cat_id'];
}
?>