个人学习总结,侵删。
1、查询表A中存在ID重复三次以上的记录,查询语句如下:
SELECT * from ( select *, count(user_id) as counts from articles GROUP BY user_id ) T where T.counts >= 3;
2、查询平均成绩大于60分的同学的学号和平均成绩;
select stuId,avg(score) from Scores group by stuId having avg(score) >60;
https://www.cnblogs.com/zqm1/p/6559757.html
3、说出以下聚合数的含义:avg ,sum ,max ,min , count ,count(*)
4、随机获取10条数据的方法
SELECT * FROM T_USER ORDER BY RAND() LIMIT 10
https://blog.csdn.net/lishimin1012/article/details/46516187
5、说明:显示文章、提交人和最后回复时间
select a.title,a.username,b.adddate from table a,(select max(adddate) adddate from table where table.title=a.title) b