题解 | #分组过滤练习题#

select university, 
avg(question_cnt) AS avg_question_cnt, 
AVG(answer_cnt) AS avg_answer_cnt
FROM user_profile
GROUP BY university
HAVING avg(question_cnt)<5 OR AVG(answer_cnt)<20

在 SQL 中增加 HAVING 子句原因是，WHERE 关键字无法与聚合函数一起使用。 HAVING 子句可以让我们筛选分组后的各组数据。 SQL HAVING 语法 SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name HAVING aggregate_function(column_name) operator value;