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MySQL: el operando debe contener 1 columna (s)
Mientras trabajaba en un sistema que estoy creando, intenté usar la siguiente consulta en mi proyecto: SELECT topics.id, topics.name, topics.post_count, topics.view_count, COUNT( posts.solved_post ) AS solved_post, (SELECT users.username AS posted_by, users.id AS posted_by_id FROM users WHERE users.id = posts.posted_by) FROM topics LEFT OUTER JOIN posts ON posts.topic_id = topics.id WHERE …