refactoring sql in php

What is a good place to put sql commands so they do not appear in the main code, how can this be done? How can sql commands such as the following be refactorised:

function select_Query($sql, $link)
{
    $query = mysqli_query($link, $sql);

    if (!$query)
    {
        echo "Failure"; #   TODO: LOG THIS
    }

    $data = array();
    while ($row = mysqli_fetch_array($query) )
    {
        $data[] = $row;
    }    

    return $data;
}


$query = select_Query("SELECT thread.title, thread.id as t_id,
                         thread.content
                         FROM thread
                         LIMIT $start, 30", $link);

How would you factorise the $query var part to generalise it for other sql statements - as that is fairly simple sql, however when several joins are used sql commands take up several lines in my code, I开发者_如何转开发 don't want to mix them with my php code.

Read about ORM and MVC. You factor it out by building a layered application, and encapsulating your data models in classes.

Check out Zend Framework I have became to worship it.