How to avoid duplicate in random query result in mysql - php

Question

I need to select 4 random ids from the table, but problem is that they are sometimes duplicated how to avoid that? I have tried to use DISTINCT but with no results here is the code.As for CMS I am using opencart.
<h1>similar products</h1>
<?php
$id = $this->customer->getCustomerGroupId();
$cur_jur = $this->db->query("SELECT `value` FROM `" . DB_PREFIX . "currency` WHERE currency_id = '1'");
$cur_fiz = $this->db->query("SELECT `value` FROM `" . DB_PREFIX . "currency` WHERE currency_id = '3'");
$max_symb = 25;
$fee_id = $product_id;
$product_sql_test_fee = $this->db->query("SELECT `category_id` FROM `" . DB_PREFIX . "product_to_category` WHERE `product_id`='".$fee_id."' ORDER BY RAND() LIMIT 0,10");
$feed_id = $product_sql_test_fee->row['category_id'];
$i=1;
$imax = 5;
$products_id = '';
while ($i < $imax)
{
$product_fee = $this->db->query("SELECT DISTINCT `product_id` FROM `" . DB_PREFIX . "product_to_category` WHERE `category_id`='".$feed_id."' AND NOT `product_id` = '".$products_id."' GROUP BY `product_id` ORDER BY RAND() LIMIT 0,10");
if(isset($product_fee->row['product_id']))
{
$pr_id[$i] = $product_fee->row['product_id'];
}
$pr_id_[$i] = $this->model_catalog_product->getProduct($pr_id[$i]);
$products_id .= $pr_id[$i].',';
$product_duplicate = explode(',',$products_id);
if ($product_duplicate[$i] == $pr_id[$i])
{
}
//if ($product_duplicate[$i] == $pr_id[$i]){ //echo 'Duplicate';
//continue;} else {
//foreach ($product_duplicate as $id) {
//if ($id == $pr_id[$i]) continue;
//}
//$price_plus = $pr_id_[$i]['price'] + ($pr_id_[$i]['price'] * 0.20);
//$price_minus = $pr_id_[$i]['price'] - ($pr_id_[$i]['price'] * 0.20);
//$price_of_product = (int)$price / $cur_fiz->row['value'];
//if ($price_of_product < $price_plus && $price_of_product > $price_minus) {
//echo $pr_id[$i].'||'.$price_minus.'||'.$price_plus.'||'.$pr_id_[$i]['price'].'||'.$price_of_product.'<br/>';
//}
$price_plus = $pr_id_[$i]['price'] + ($pr_id_[$i]['price'] * 0.30);
$price_minus = $pr_id_[$i]['price'] - ($pr_id_[$i]['price'] * 0.30);
$price_of_product = (int)$price / $cur_fiz->row['value'];
if ($price_of_product < $price_plus && $price_of_product > $price_minus )
{
}
}
?>

Answer 1

You have to use group by category_id problem will be resolved.
SELECT DISTINCT `product_id` FROM `" . DB_PREFIX . "product_to_category` WHERE `category_id`='".$feed_id."' AND NOT `product_id` = '".$products_id."' GROUP BY `category_id`