Running 2 database querys from an array - php

Question

I am trying to run 2 database querys the second using an array from the first, any one have any ideas why this stops the page from loading?
$query = $this->db->query("SELECT category_id FROM listings WHERE listing_id = '1' LIMIT 1");
foreach ($query->result() as $row)
{
$query2 = $this->db->query("SELECT listing_title FROM listings WHERE listing_type = '".$row->category_id."' ORDER BY RAND() LIMIT 2");
foreach ($query2->result() as $row)
{
echo $row->listing_title;
}
}

Answer 1

You are overwriting the outer $row in your inner loop
$query = $this->db->query("SELECT category_id FROM listings WHERE listing_id = '1' LIMIT 1");
foreach ($query->result() as $row)
{
$query2 = $this->db->query("SELECT listing_title FROM listings WHERE listing_type = '".$row->category_id."' ORDER BY RAND() LIMIT 2");
foreach ($query2->result() as $row2) // <--- $row2 not $row
{
echo $row2->listing_title;
}
}

Answer 2

Try this:
(Take advantage of prepare statements, the prepare() function, etc)
$query = "SELECT category_id FROM listings WHERE listing_id = '1' LIMIT 1;";
$query2 = "SELECT listing_title FROM listings WHERE listing_type = :categoryId ORDER BY RAND() LIMIT 2;";
$db = $this->db;
$statement = $db->prepare($query);
$statement->execute();
$statement->setFetchMode(PDO::FETCH_ASSOC);
while($row = $statement->fetch())
{
$categoryId = $row['category_id'];
$statement2 = $db->prepare($query2);
$statement2->execute(array(':categoryId' => $categoryId));
$statement2->setFetchMode(PDO::FETCH_ASSOC);
while($row2 = $statement2->fetch())
{
$listingTitle = $row2['listing_title'];
echo $listingTitle;
}
}

Answer 3

This is not very good code. Why use a foreach loop when the Select query has Limit 1?
Since you are going for a category id where listing_id=1 (with LIMIT 1), your code could just be shortened to:
SELECT listing_title FROM listings WHERE listing_id=1 ORDER BY RAND() LIMIT 2
Also, ORDER BY RAND() is a big resource killer on large tables. I recommend finding a more proper way to order your results.
EDIT: Full code that I would use:
$db=$this->db; //Just so we don't have to keep referencing $this (assuming you are not in a class)
$sql="SELECT listing_title
FROM listings
WHERE listing_id=?
ORDER BY RAND()
LIMIT 2";
$statement=$db->prepare($sql);
$statement->execute(array(1));
while($result=$statement->fetchObject()){
echo $result->listing_title;
}