Custom select query from 2 categories

i tried to make a custom select query to get a post based on 2 categories.
The code that i get from wordpress works for 1 category, but not 2.

SELECT DISTINCT wposts.*
		FROM $wpdb->posts wposts
			LEFT JOIN $wpdb->postmeta wpostmeta ON wposts.ID = wpostmeta.post_id
			LEFT JOIN $wpdb->term_relationships ON (wposts.ID = $wpdb->term_relationships.object_id)
			LEFT JOIN $wpdb->term_taxonomy ON ($wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id)
			LEFT JOIN $wpdb->terms ON ($wpdb->terms.term_id = $wpdb->term_taxonomy.term_id)
		WHERE $wpdb->term_taxonomy.taxonomy = 'category'
			AND $wpdb->terms.name = '" . $selectedCategory . "'
		ORDER BY wposts.ID DESC

That’s the code that i’m using, but i don’t know how to add the 2nd category into the query.
Please help..