答案来啦！学习SQL第一天 2020.0204

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#1 Created at ... [Delete] [Delete and Lock User]

SELECT class_id,AVG(score) FROM students GROUP BY class_id

SELECT class_id,gender,AVG(score) FROM students GROUP BY class_id,gender

#2 Created at ... [Delete] [Delete and Lock User]

请教一个问题：如何对返回结果进行进一步的排序

#3 Created at ... [Delete] [Delete and Lock User]

直接使用 ORDER 进行排序就行了

SELECT class_id, gender gen, AVG(score) average, COUNT(*) num from students GROUP by class_id, gender ORDER by average;

#4 Created at ... [Delete] [Delete and Lock User]

select class_id, gender, avg(score) average from students group by class_id, gender order by class_id desc,gender desc,average desc;