ToyVoyagers has exited with an error

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You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AND t.topic_id = p.post_topic AND p.post_author != t.topic_sta' at line 6

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Query Error [1064]:
This type of error is reported by MySQL.

Query:
SELECT DISTINCT u.user_name, u.user_id FROM mb_posts p , mb_topics t , mb_users u WHERE p.post_topic = AND t.topic_id = p.post_topic AND p.post_author != t.topic_starter AND p.post_author = u.user_id ORDER BY p.post_time

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