求一sql,不算难，但小弟写不出来

Question

在oracle里面有张新闻评论表如下：主键评论信息id    每条新闻的id    评论的标题   评论的内容  
com_id             key_id          com_title   com_content   
1                   3              title1      content1 
2                   3              title2      content2
3                   3              title3      content3
4                   7              title4      content4
5                   7              title5      content5
6                   9              title6      content6
7                   9              title7      content7
8                   9              title8      content8
9                   9              title9      content9
10                  8              title10     content10
11                  8              title11     content11
12                  8              title12     content12
13                  8              title13     content13
14                  8              title14     content14
15                  8              title15     content15这里有15条评论信息，记录了对key_id为3，7，9，8新闻的评论信息，现在我要求前3条评论信息最多的新闻key_id，查出来的结果应该是：key_id
8        //它有6条评论
9        //它有4条评论
3        //它有3条评论

Answer 1

select key_id from(
  select key_id,count(1) c from tab1
    group by key_id
    order by c desc) 
  where  rowid<=3

Answer 2

晕，写错了
select key_id from(
  select key_id,count(1) c from tab1
    group by key_id
    order by c desc) 
  where  rownum<=3

Answer 3

感觉count(*)应该是可以的，就不知道count(1)里面的1是什么意思？

Answer 4

count(*)效果是一样的
count(1)里面的1可以用任意数字或字符串代替。
每行记录都返回一个1
count会计算'1'的个数，也就是记录的条数

Answer 5

select key_id from(select key_id,count(com_id) count_id from t1 group by key_id order by count_id desc) where rownum<=3