Here is pretty straight forward mysql query to get WordPress post categories. I’ve excluded the default Uncategorized category.
SELECT wt.*, wtt.taxonomy FROM wp_terms wt inner join wp_term_relationships wtr on wtr.term_taxonomy_id = wt.term_id inner join wp_term_taxonomy wtt on wtt.term_taxonomy_id = wtr.term_taxonomy_id where wt.term_id <> 1 and wtr.object_id = 1
“wt.term_id <> 1″ to exclude Uncategorized Category and “wtr.object_id = 1” to get categories for post id 1.