PDO: Invalid parameter number: mixed named and positional parameters

Question

I have come across this warning I've not seen before:

Warning: PDOStatement::execute() [pdostatement.execute]: SQLSTATE[HY093]: Invalid parameter number: mixed named and positional parameters in...

Referring to the following PDO query (have simplified the function for ease of reading):

$offset = 0;
$limit = 12;
function retrieve_search_posts($searchfield, $offset, $limit){


        $where = array();

        $words = preg_split('/[\s]+/',$searchfield);

        array_unshift($words, '');
        unset($words[0]);

        $where_string = implode(" OR ", array_fill(0,count($words), "`post_title` LIKE ?"));

        $query = "
                                SELECT  p.post_id, post_year, post_desc, post_title, post_date, img_file_name, p.cat_id
                                FROM    mjbox_posts p
                                JOIN    mjbox_images i
                                ON      i.post_id = p.post_id
                                        AND i.cat_id = p.cat_id
                                        AND i.img_is_thumb = 1
                                        AND post_active = 1
                                WHERE $where_string
                                ORDER BY post_date
                                LIMIT :offset, :limit
                                DESC";
        $stmt = $dbh->prepare($query);

        foreach($words AS $index => $word){
            $stmt->bindValue($index, "%".$word."%", PDO::PARAM_STR);
        }
        $stmt->bindParam(':offset', $offset, PDO::PARAM_INT);
        $stmt->bindParam(':limit', $limit, PDO::PARAM_INT);
        $stmt->execute();

        $searcharray = $stmt->fetchAll(PDO::FETCH_ASSOC);

        return $searcharray;
    }

The function and PDO query works fine without the offset and limit variables included in the query. So what might be causing this warning?

Thanks

Answer 1

Change

LIMIT :offset, :limit

to

LIMIT ?, ?

and

$stmt->bindParam(':offset', $offset, PDO::PARAM_INT);
$stmt->bindParam(':limit', $limit, PDO::PARAM_INT);

to:

$stmt->bindValue($index+1, $offset, PDO::PARAM_INT);
$stmt->bindValue($index+2, $limit, PDO::PARAM_INT);

Answer 2

in your where_string you use ? that is a positional parameter and in your limit and offset you use : that is a named parameter that is causing the warning don't mix them