题解 | #分组过滤练习题#

SELECT university, ROUND(AVG(question_cnt),3) AS avg_question_cnt,ROUND(AVG(answer_cnt),3) AS avg_answer_cnt
FROM user_profile
GROUP BY university
HAVING avg_question_cnt<5 OR avg_answer_cnt <20

问题拆解：

1. 要输出什么内容：university, ROUND(AVG(question_cnt),3) AS avg_question_cnt,ROUND(AVG(answer_cnt),3) AS avg_answer_cnt
2. 从哪里输出：FROM user_profile
3. 聚合函数的计算是按哪一列计算的：GROUP BY university
4. 筛选条件是什么：HAVING avg_question_cnt<5 OR avg_answer_cnt <20

我认为大多数题目在求解时都可以先问自己这几个问题，然后根据SQL的常见模式填充补充细节即可！