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SELECT p.ID FROM wp_posts AS p INNER JOIN wp_term_relationships AS tr ON p.ID = tr.object_id INNER JOIN wp_term_taxonomy AS tt ON tr.term_taxonomy_id = tt.term_taxonomy_id WHERE p.post_type = 'post' AND tt.taxonomy = 'category' AND tt.term_id IN (6) AND p.ID NOT IN ( SELECT tr.object_id FROM wp_term_relationships tr LEFT JOIN wp_term_taxonomy tt ON (tr.term_taxonomy_id = tt.term_taxonomy_id) WHERE p.post_status = 'publish' ORDER BY p.post_date DESC LIMIT 1