How to retrieve a value from database with $wpdb

Sample SQL query used:

global $wpdb;
	$result = "";
	$query = ("SELECT
		sum($wpdb->postmeta.meta_value)
		FROM $wpdb->posts
		INNER JOIN $wpdb->postmeta
		ON $wpdb->posts.id = $wpdb->postmeta.post_id
		WHERE post_status = 'publish' && post_type = 'cases'
		GROUP BY meta_key
		LIKE '%negative%'
		");

	$result = $wpdb->get_results( $query, ARRAY_N );
	echo $result[1][0];