1.按照一个列或者多个列对数据分组
2.对每个组进行聚合操作
3. 对聚合后的结果进行判断
1. select avg(score) as score from teacher
2. select grade, avg(score) as avg_score from teacher group by grade
3. select grade, avg(score) as avg_score from teacher group by grade having avg_score>30;
原文：https://www.cnblogs.com/hapyygril/p/11108998.html