Cannot generate the report - php

Question

I want to generate the report that click and choose from the category drop down list, then it will show that the order which product in the category that you select and how many of them sold. But it cannot come out, I have been find many times the errors, and I also tried the query in SQL as it showed correct. I don't know why. Please help me.
<?php
session_start();
include_once 'header_admin.php';
?>
<div class="report">
<h2>Sales Report</h2>
<div class="sales_report">
<form action="" method="POST">
<select name="category" class="category">
<option>Category</option>
<?php
include_once 'includes/dbh.php';
$query1 = "SELECT * from category";
$result1 = mysqli_query($conn, $query1);
while ($row1 = mysqli_fetch_assoc($result1)) {
$CategoryID = $row1['CategoryID'];
$rowData1 = $row1['CategoryName'];
?>
<option value="<?php echo $CategoryID; ?>"><?php echo $rowData1; ?></option>
<?php
}
?>
</select>
<button class="generate" type="submit" name="generate">Generate</button>
<table class="genreport">
<tr>
<th>Furniture ID</th>
<th>Furniture Name</th>
<th>Category Name</th>
<th>Order Date</th>
<th>Quantity</th>
<th>Total Amount</th>
</tr>
<?php
if (isset($_POST['generate'])) {
$catName = mysqli_real_escape_string($conn, $_POST['category']);
$query2 = "SELECT D.FurCode, F.FurName, C.CategoryName, O.OrderDate, D.quantity, COUNT(D.quantity * D.PriceEach)
FROM orderdetail D, furniture F, category C, ordertab O
WHERE C.CategoryName = '$catName' GROUP BY C.$catName ORDER BY C.$catName ";
$result2 = mysqli_query($conn, $query2);
if ($result2) {
while ($row2 = mysqli_fetch_array($result2)) {
$furCode = $row2['FurCode'];
$furName = $row2['FurName'];
$orderDate = $row2['OrderDate'];
$quantity = $row2['quantity'];
$priceEach = $row2['PriceEach'];
$total = $quantity * $priceEach;
?>
<tr>
<td><?php echo $furCode; ?></td>
<td><?php echo $furName; ?></td>
<td><?php echo $catName; ?></td>
<td><?php echo $orderDate; ?></td>
<td><?php echo $quantity; ?></td>
<td><?php echo $total; ?></td>
</tr>
<?php
}
}
} else {
echo '<tr><td>No Result!</td><td></td><td></td><td></td><td></td><td></td></tr>';
}
?>
</table>
</form>
</div>
</div>
</div>
</section>
</body>
</html>