need help with a custom query

$querystr = "
	SELECT DISTINCT wposts.*
	FROM $wpdb->posts wposts
	LEFT JOIN $wpdb->term_relationships ON (wposts.ID = $wpdb->term_relationships.object_id)
	WHERE wposts.post_status = 'publish'
	AND wposts.post_type = 'post' AND wposts.ID IN (
		SELECT DISTINCT object_id
		FROM $wpdb->term_relationships
		WHERE $wpdb->term_relationships.term_taxonomy_id = 3)
			".(!empty($_POST['search']['city']) ?
			"AND wposts.ID IN (
				SELECT DISTINCT object_id FROM $wpdb->term_relationships
				WHERE $wpdb->term_relationships.term_taxonomy_id = ".$_POST['search']['city'].")":"")."
			".(!empty($_POST['search']['service']) ?
			"AND wposts.ID IN (
				SELECT DISTINCT object_id FROM $wpdb->term_relationships
				WHERE $wpdb->term_relationships.term_taxonomy_id = ".$_POST['search']['service'].")":"")."
			".(!empty($_POST['search']['budget']) ?
			"AND wposts.ID IN (
				SELECT object_id
				FROM wp_term_relationships
				WHERE term_taxonomy_id IN (
					SELECT term_taxonomy_id
					FROM wp_term_taxonomy
					WHERE term_id = ".$_POST['search']['budget']." AND taxonomy = 'post_tag'))":"")."
	ORDER BY wposts.post_date DESC";

$pageposts = $wpdb->get_results($querystr, OBJECT);

Hey guys,
Im trying to create a custom post search/filter query on my site. Basically all the posts belong to 3 categories, and will have certain tags. All posts will share one category (3, hardcoded), the other 2 can be different between posts and are provided by $_POSTs.

The problem im having is that $_POST[‘search’][‘service’] cause the query to not work. If only $_POST[‘search’][‘budget’] and $_POST[‘search’][‘city’] are provided, then its fine. Anyone know if there’s an easy solution? thansk.