第一题:
SELECT class_id, AVG(score) score FROM students GROUP BY class_id;
第二题:
SELECT class_id,gender, AVG(score) score FROM students GROUP BY class_id,gender;
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NahuyeuY
第一题:
SELECT class_id, AVG(score) score FROM students GROUP BY class_id;
第二题:
SELECT class_id,gender, AVG(score) score FROM students GROUP BY class_id,gender;