SELECT class_id ,AVG (score) average FROM students GROUP BY class_id
SELECT class_id, gender, AVG(score) FROM students GROUP BY class_id, gender;
参考了别人的 有点难
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岸边到底
SELECT class_id ,AVG (score) average FROM students GROUP BY class_id
SELECT class_id, gender, AVG(score) FROM students GROUP BY class_id, gender;
参考了别人的 有点难