Question

Please see the data tables and query below ..

Items
Id, Name
1, Item 1
2, Item 2

Categories
Id, Name, Parent ID
1, Furniture , 0
2, Tables, 1
3, Beds, 1
4, Dining Table, 2
5, Bar Table, 2
4, Electronics, 0
5, Home, 4
6, Outdoors, 4
7, Table lamp, 4

ItemCategory
ItemId, CategoryId
1, 2 .. Row1
2, 4 .. Row 2
2, 5 .. Row 3 

ItemCategory table stores which items belongs to which category. An item can belong to top level and or sub category. there are about 3 level deep categories, that is, Tob level, sub level, and sub sub level.

Users select all of the categories they want to view and submit and I can query the database by using a sample query below..

    SELECT * FROM items i INNER JOIN ItemCategory ic ON 
ic.itemId = i.itemId AND ic.itemId IN ('comma separated category ids')

This works fine.

My question is that Is it possible to view all the items under a top level category even though it has not been directly assigned to the item. For example, if users select Furniture above, then it lists all the items belonging to its sub categories (even though the ItemCategory doesn’t contain any record for it)??

I’m open to making necessary amendements to the data table or queries, please suggest a solution. Thank you.

Answer 1

Watcher has given a good answer, but I’d alter my approach somewhat to the following, so you have a structured recursive 2-dimensional array with categories as keys and items as values. This makes it very easy to print back to the user when responding to their search requirements.

Here is my approach, which I have tested:

$items = getItemsByCategory($topCategory);
//To print contents
print_r($items);

function getItemsByCategory($sid = 0) {
  $list = array();
  $sql = "SELECT Id, Name FROM Categories WHERE ParentId = $sid";
  $rs = mysql_query($sql);
  while ($obj = mysql_fetch_object($rs)) {
    //echo $obj->id .", ".$parent." >> ".$obj->name."<br/>";
    $list[$obj->name] = getItems($obj->id);
    if (hasChildren($obj->id)) {
        array_push($list[$obj->name],getItemsByCategory($obj->id));
    }
  }
  return $list;
}

function getItems($cid) {
  $list = array();
  $sql = "SELECT i.Id, i.Name FROM Items p INNER JOIN ItemCategory ic ON i.id = ic.ItemId WHERE ic.CategoryId = $cid";
  $rs = mysql_query($sql);
  while ($obj = mysql_fetch_object($rs)) {
    $list[] = array($obj->id, $obj->name);
  }
  return $list;
}

function hasChildren($pid) {
  $sql = "SELECT * FROM Categories WHERE ParentId = $pid";
  $rs = mysql_query($sql);
  if (mysql_num_rows($rs) > 0) {
    return true;
  } else {
    return false;
  }
}

Hope this helps.