一个关于SQL 查询的问题 求助

[lgq1314]

读者reader(userid,u_name) 图书book(bookid,b_name) 借阅记录lend(recordid,userid,bookid,date) 要搜出 借书最多的五位读者的姓名和借阅册数

[vivianfdlpw]

select top 5
B.u_name
,count(1) as '借阅册数'

from lend A
join reader B on A.userid=B.userid
join book C on B.bookid=C.bookid
group by B.userid,B.u_name
order by count(1) desc

[zouqiang122]

support~~~

[lgq1314]

应该是这样的吧
select top 5
B.u_name
,count(1) as '借阅册数'

from lend A
join reader B on A.userid=B.userid
join book C on A.bookid=C.bookid
group by B.userid,B.u_name
order by count(1) desc
1：count(1)表示什么 它是从那个表中取出的字段呢？
2：为什么按照B.userid 分组

[lgq1314]

如果 要查 阅查被借次数最多的书名，被借次数 应该如何 谢谢