Querying Main Site Post Table On Sub Site Using $wpdb


I'm trying to run a query from the main sites post table onto the sub site, but I think how the table prefixes are set is screwing with me a bit. I figure if I wanted to query the from different blogs I would just use the prefixes like so.
Ex :
Mainsite: SELECT $wpdb->posts.*
Blog 2: SELECT $wpdb->2_posts.*

But it turns out when I run this query on blog 2 I get the posts from that site:

$querystr = "
    SELECT $wpdb->posts.*
    FROM $wpdb->posts
    WHERE $wpdb->posts.post_type =    'post'
    AND $wpdb->posts.post_status =   'publish'
    ORDER BY $wpdb->posts.post_date DESC

Any ideas how to achieve what I want without the use of switch_to_blog();

Thank you for your help!