SET variable on codeigniter SQL

Question

I've tried this code:

SET @num := 0, @type := NULL;
SELECT categories_name, products_name, products_url, categories_id, 
       @num := IF( @type = categories_name, @num +1, 1 ) AS row_number,
       @type := categories_name AS dummy
  FROM (
        SELECT categories_name, products_name, products_url, ptc.categories_id
          FROM toc_products_description pd
         INNER JOIN toc_products_to_categories ptc ON pd.products_id = ptc.products_id
         INNER JOIN toc_categories_description cd ON cd.categories_id = ptc.categories_id
               AND pd.language_id =1
               AND cd.language_id =1
        ) AS x
 GROUP BY x.categories_name, x.products_name, x.products_url, x.categories_id
HAVING row_number <=2

On SQL (and work well), and now I need this code to be implemented on codeigniter with query(). The problem is I can't insert

SET @num := 0, @type := NULL;

On query(), because it's always give error messages when I inserted it.

I have done this:

$query="SELECT categories_name, products_name, products_url, categories_id, @num := IF( @type := categories_name, @num +1, TRUE) AS row_number, @type := categories_name AS dummy
                FROM (
                SELECT categories_name, products_name, products_url, ptc.categories_id
                FROM toc_products_description pd
                INNER JOIN toc_products_to_categories ptc ON pd.products_id = ptc.products_id
                INNER JOIN toc_categories_description cd ON cd.categories_id = ptc.categories_id
                AND pd.language_id =1
                AND cd.language_id =1
                ) AS x
                GROUP BY x.categories_name, x.products_name, x.products_url, x.categories_id
                HAVING row_number <=5";        
        $result = $this->db->query($query);

and I cant write anything before SELECT syntax because it will return error message when I try it.

Answer 1

You will have to run two seperate queries for this

$query  =   "SET @num := 0, @type := NULL";
$this->db->query($query);
$new_query  =   "
                SELECT categories_name, products_name, products_url, categories_id, 
                       @num := IF( @type = categories_name, @num +1, 1 ) AS row_number,
                       @type := categories_name AS dummy
                  FROM (
                        SELECT categories_name, products_name, products_url, ptc.categories_id
                          FROM toc_products_description pd
                         INNER JOIN toc_products_to_categories ptc ON pd.products_id = ptc.products_id
                         INNER JOIN toc_categories_description cd ON cd.categories_id = ptc.categories_id
                               AND pd.language_id =1
                               AND cd.language_id =1
                        ) AS x
                 GROUP BY x.categories_name, x.products_name, x.products_url, x.categories_id
                HAVING row_number <=2";
$this->db->query($new_query);