How To Execute Totally Separate Query

Dear All,

Can you please advise how to execute a different query in wordpress it always takes the following :-

SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts WHERE….

I have used the following to change the current query :-

$GLOBALS['wp_query'] = new WP_Query();
return $GLOBALS['wp_query']->query($query);

But still query remains same no changes can be seen. I want a query like SELECT wp_postmeta.post_id FROM wp_postmeta, wp_posts WHERE…

Can any one help?

Thanks
Kaushal