CREATE TABLE `students` (
             `id` int NOT NULL AUTO_INCREMENT,
             `name` varchar(255) NOT NULL,
             `age` int NOT NULL,
             PRIMARY KEY (`id`)
             ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4

CREATE TABLE `scores` (
           `student_id` int NOT NULL,
           `subject` varchar(255) NOT NULL,
           `score` int NOT NULL,
           PRIMARY KEY (`student_id`, `subject`),
           KEY `student_id` (`student_id`),
           CONSTRAINT `scores_ibfk_1` FOREIGN KEY (`student_id`) REFERENCES `students` (`id`)
           ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4

题解：

SELECT s.age
FROM students s
JOIN (
    SELECT student_id, AVG(score) AS avg_score
    FROM scores
    GROUP BY student_id
) sc ON s.id = sc.student_id
GROUP BY s.age
HAVING COUNT(s.id) > 2
   AND AVG(sc.avg_score) > 60;