摘要：
根据book_id,class_id确定老师uidselect user_idfrom lessonsleft join book on lessons.lesson_id = book.lesson_idwhere lessons.class_id = 2and book.id = 1group by user_id;根据book_id,class_id,semester_id确定老师uidselect user_idfrom lessonsleft join book on lessons.lesson_id = book.lesson_idwhere lessons.class_id = 阅读全文