1. 在users表中查询注册时间最早的十条会员信息。
select * from users order by cdate asc limit 10;

2. 从两个表中查询点赞数最高的5条博客信息，要求显示字段：（博文id，标题，点赞数，会员名）
select b.id as blogid,b.title,b.pcount,u.name as username from blog as b,users as u where b.uid=u.id order by pcount desc limit 5;

3. 统计每个会员的发表博文数量（降序），要求显示字段（会员id号，姓名，博文数量）
select u.id as userid,u.name as username,count(*)as blogcount from blog as b,users as u where b.uid=u.id group by b.uid order by blogcount desc;

4. 获取会员的博文平均点赞数量最高的三位。显示字段（会员id，姓名，平均点赞数）
select u.id as userid,u.name as username,avg(pcount) as avgpcount from blog as b,users as u where b.uid=u.id group by b.uid order by avgpcount desc limit 3;

5. 删除没有发表博文的所有会员信息。
delete from users where id not in (select uid from blog);