operand should contain 1 columns [duplicate]
This question already has an answer here: Operand Should Contain 1 Column - MySQL NOT IN 2 answers SELECT topic_id FROM phpbb_topics AS t WHERE t.topic_id IN ( SELECT p.topic_id, COUNT(p.post_id) AS total_posts FROM phpbb_posts AS p WHERE p.poster_id = 61640 GROUP BY p.topic_id HAVING t.topic_replies_real = total_posts - 1 ); That query gets me the following error: Error Code: 1241. Operand should contain 1 column(s) Any ideas? You shouldn't include COUNT(p.post_id) AS total_posts in SELECT list in your subquery. Just SELECT topic_id FROM phpbb_topics AS t WHERE t.topic_id IN ( SELECT p.topic