ID  Item_id
1   1
2   2
3   3
4   4
5   5

ID Item_id Category
   1   1      cat1
   2   2      cat1
   3   2      cat2
   4   3      cat2
   5   3      cat3
   6   3      cat4
   7   4      cat2
   8   5      cat1
   etc.

Category_id  category_name
cat1        apples
cat2        oranges
cat3        bananas
cat4        pineapples

public function getCategories(){
$this->db->query('SELECT table1.*, table2.*, table3.*
       FROM table1
       INNER JOIN table2
       ON table1.item_id = table2.item_id
       INNER JOIN table3
       ON table2.category=table3.category_id');

$results = $this->db->resultset();
return $results;}

$items = $offer_class -> getCategories();

<?php foreach($items as $item){
echo $item->category_name;
}
?>