select number
from grade
group by number
having count(*)>=3

having 和 where 的区别https://www.huaweicloud.com/articles/00d8b9053add55b50c807934f79ee0d2.html#:~:text=SQL%E4%B8%ADWhere%E4%B8%8EHaving%E7%9A%84%E5%8C%BA%E5%88%AB.%20%E3%80%90%E6%91%98%E8%A6%81%E3%80%91%22Where%22%20%E6%98%AF%E4%B8%80%E4%B8%AA%E7%BA%A6%E6%9D%9F%E5%A3%B0%E6%98%8E%EF%BC%8C%E4%BD%BF%E7%94%A8Where%E6%9D%A5%E7%BA%A6%E6%9D%9F%E6%9D%A5%E4%B9%8B%E6%95%B0%E6%8D%AE%E5%BA%93%E7%9A%84%E6%95%B0%E6%8D%AE%EF%BC%8CWhere%E6%98%AF%E5%9C%A8%E7%BB%93%E6%9E%9C%E8%BF%94%E5%9B%9E%E4%B9%8B%E5%89%8D%E8%B5%B7%E4%BD%9C%E7%94%A8%E7%9A%84%EF%BC%8C%E4%B8%94Where%E4%B8%AD%E4%B8%8D%E8%83%BD%E4%BD%BF%E7%94%A8%E8%81%9A%E5%90%88%E5%87%BD%E6%95%B0%E3%80%82.%20%22Having%22%E6%98%AF%E4%B8%80%E4%B8%AA%E8%BF%87%E6%BB%A4%E5%A3%B0%E6%98%8E%EF%BC%8C%E6%98%AF%E5%9C%A8%E6%9F%A5%E8%AF%A2%E8%BF%94%E5%9B%9E%E7%BB%93%E6%9E%9C%E9%9B%86%E4%BB%A5%E5%90%8E%E5%AF%B9%E6%9F%A5%E8%AF%A2%E7%BB%93%E6%9E%9C%E8%BF%9B%E8%A1%8C%E7%9A%84%E8%BF%87%E6%BB%A4%E6%93%8D%E4%BD%9C%EF%BC%8C%E5%9C%A8Having%E4%B8%AD%E5%8F%AF%E4%BB%A5%E4%BD%BF%E7%94%A8%E8%81%9A%E5%90%88%E5%87%BD%E6%95%B0%E3%80%82.%20%E5%9C%A8%E8%AF%B4%E5%8C%BA%E5%88%AB%E4%B9%8B%E5%89%8D%EF%BC%8C%E5%BE%97%E5%85%88%E4%BB%8B%E7%BB%8DGROUP,BY%E8%BF%99%E4%B8%AA%E5%AD%90%E5%8F%A5%EF%BC%8C%E8%80%8C%E5%9C%A8%E8%AF%B4GROUP%E5%AD%90%E5%8F%A5%E5%89%8D%EF%BC%8C%E5%8F%88%E5%BE%97%E5%85%88%E8%AF%B4%E8%AF%B4%22%E8%81%9A%E5%90%88%E5%87%BD%E6%95%B0%22--SQL%E8%AF%AD%E8%A8%80%E4%B8%AD%E4%B8%80%E7%A7%8D%E7%89%B9%E6%AE%8A%E7%9A%84%E5%87%BD%E6%95%B0%E3%80%82.%20%E4%BE%8B%E5%A6%82SUM...%20%22Where%22%20%E6%98%AF%E4%B8%80%E4%B8%AA%E7%BA%A6%E6%9D%9F%E5%A3%B0%E6%98%8E%EF%BC%8C%E4%BD%BF%E7%94%A8Where%E6%9D%A5%E7%BA%A6%E6%9D%9F%E6%9D%A5%E4%B9%8B%E6%95%B0%E6%8D%AE%E5%BA%93%E7%9A%84%E6%95%B0%E6%8D%AE%EF%BC%8CWhere%E6%98%AF%E5%9C%A8%E7%BB%93%E6%9E%9C%E8%BF%94%E5%9B%9E%E4%B9%8B%E5%89%8D%E8%B5%B7%E4%BD%9C%E7%94%A8%E7%9A%84%EF%BC%8C%E4%B8%94Where%E4%B8%AD%E4%B8%8D%E8%83%BD%E4%BD%BF%E7%94%A8%E8%81%9A%E5%90%88%E5%87%BD%E6%95%B0%E3%80%82.%20

简单来说就是where在聚合前 having在聚合后~