Indicating checkbox values from MySQL/PHP - php

Question

I have 4 MySQL tables:
properties (these are properties)
id | address | price
1 | 123 St. | 100,000
2 | 456 St. | 200,000
categories (these are categories of amenities for properties)
id | title
1 | Kitchen
2 | Entertainment
items (these are items under the categories above)
id | catid | item
1 | 1 | Stove
2 | 1 | Fridge
3 | 2 | TV
4 | 2 | Couch
propertyamenities (these are the particular amenities for a property)
id | listingid | amenityid
1 | 1 | 3
2 | 1 | 4
I have built a form where the user can select the various amenities for a given property using checkboxes, which inserts from PHP into MySQL tables above.
I now need to allow the user to edit the amenities (using checkboxes) for a given property. The code I am currently using is:
$result = mysqli_query($con,"SELECT DISTINCT a.title AS maincategory, b.item AS smallcategory, b.id as itemid FROM categories a, items b WHERE a.id = b.catid ORDER BY maincategory ASC, smallcategory ASC") or die(mysqli_error($con));
// keep track of previous maincategory
$previous_maincategory = NULL;
while ($row = mysqli_fetch_assoc($result))
{
// if maincategory has changed from previouscategory then display it
if ($previous_maincategory != $row['maincategory']) {
echo '<tr>
<td colspan="2" valign="top"><strong>';
echo $row['maincategory'];
echo '</strong></td>
</tr>';
}
echo "<tr>";
echo "<td>";
echo "<input type='checkbox' name='amenities[]' value='".$row['itemid']."'>".$row['smallcategory'];
echo "</td>";
echo "</tr>";
// record what the previous category was
$previous_maincategory = $row['maincategory'];
}
This displays the categories and the items as checkboxes. I'm not sure how for a given property, to modify this script and have the associated checkboxes "checked". I presume I need to add in the propertyamenities table to the query, and a WHERE clause to indicate which property (e.g.,1) is being edited, but not sure how to add in the third table.
EDIT
I am closer, but it is returning the same item twice.
$result = mysqli_query($con,"SELECT DISTINCT a.title AS maincategory, b.item AS smallcategory, b.id as itemid, c.amenityid as amenity FROM categories a, items b, propertyamenities c WHERE a.id = b.catid and c.listingid = '$id' ORDER BY maincategory ASC, smallcategory ASC") or die(mysqli_error($con));
// keep track of previous maincategory
$previous_maincategory = NULL;
$myprevious_maincategory = NULL;
while ($row = mysqli_fetch_assoc($result))
{
// if maincategory has changed from previouscategory then display it
if ($previous_maincategory != $row['maincategory']) {
echo '<tr>
<td colspan="2" valign="top"><strong>';
echo $row['maincategory'];
echo '</strong></td>
</tr>';
}
echo "<tr>";
echo "<td>";
if ($row['amenity'] == $row['itemid'])
{
echo "<input type='checkbox' name='amenities[]' value='".$row['itemid']."' checked>".$row['smallcategory'];
}
else
{
echo "<input type='checkbox' name='amenities[]' value='".$row['itemid']."'>".$row['smallcategory'];
}
echo "</td>";
echo "</tr>";
// record what the previous category was
$previous_maincategory = $row['maincategory'];
}
?>
EDIT
Screenshot of current state:

Answer 1

Here is a possible solution:
/* Arrays will be used to store the property address and amenity ids */
/* in order to check against undesired duplicate echoing. */
$arr_address = [];
$arr_amenity_ids = [];
/* The four tables are joined here to get the required fields. */
/* Here, let $pid be the id of the property being considered: */
$s = "SELECT a.address as Address, b.title as Amenity, c.item as Item, b.id, c.id FROM properties a JOIN categories b JOIN items c JOIN propertyamenities d ON b.id = c.catid AND a.id = d.listingid AND c.id = d.amenityid AND a.id = '$pid';";
$q = mysqli_query($con,$s);
while(list($address, $amenity, $item, $amenity_id, $item_id) = mysqli_fetch_array($q)){
/* Can have a heading for the property address */
if(!in_array($address, $arr_address)){
echo '<h2>Property Address: '.$address.'</h2>'; $arr_address[] = $address;
}
/* A heading for each amenity once: */
if(!in_array($amenity_id,$arr_amenity_ids)){
echo '<strong>'.$amenity.'</strong>'; $arr_amenity_ids[] = $amenity_id;
}
echo '<br/><input type="checkbox" value="'.$item_id.'"/> '.$item;
}