where in 多个字段事例

查找同一学员购买的同一个课程并且订单数大于2的订单

SELECT
    order_id,
    class_id,
    student_id 
FROM
    tb_package_student 
        WHERE
            ( class_id, student_id ) IN ( SELECT class_id, student_id FROM tb_package_student GROUP BY class_id, student_id HAVING COUNT( * ) > 2 ) 
    ORDER BY
        class_id DESC;