题解 | #分组过滤练习题#

SELECT university,avg(question_cnt),avg(answer_cnt) from user_profile group by university having (avg(question_cnt) < 5) or (avg(answer_cnt) < 20);

1. 分析需要的数据：学校，提问平均数，回答平均数
2. 要求：平均提问低于5条 或者 回答平均低于20条

显示需要的数据,根据学校分组：
SELECT university,avg(question_cnt),avg(answer_cnt) from user_profile group by university;

having相当于where是条件判断。having只能在group by分组后使用。
SELECT university,avg(question_cnt),avg(answer_cnt) from user_profile group by university having (avg(question_cnt) < 5) or (avg(answer_cnt) < 20);