★小白每天一问：一条查询语句,望前辈指点

[lanytin]

BookInfo 表是图书信息表，如下：

Id
Category
Name
...

LoanBook 表是借阅表，如下：

Id
BookId //外键
userId
...

现在想取得借出书最多的书的信息和分别的借阅次数，
于是自己写的一个存储过程如下：

create procedure SelectLendingList
@qty int
as
begin 
   select top (@qty) *,BookId,num from BookInfo where BookInfo.Id=BookId and BookId
   in(select BookId ,count(distinct(BookId)) as num  from LoanBook group by BookId order by num desc)
end

但是出现了下面错误：
除非另外还指定了 TOP 或 FOR XML，否则，ORDER BY 子句在视图、内联函数、派生表、子查询和公用表表达式中无效。
还望高手纠正，和支持上述错误原因，感激涕零

[htl258_Tony]

create procedure SelectLendingList
@qty int
as
begin 
   select top (@qty) *,BookId,num from BookInfo where BookInfo.Id=BookId and BookId
   in(select top 100 percent BookId ,count(distinct(BookId)) as num  from LoanBook group by BookId order by num desc)
end

[jinjazz]

create procedure SelectLendingList @qty int as begin select top (@qty) *,BookId,num from BookInfo where BookInfo.Id=BookId and BookId in(select BookId ,count(distinct(BookId)) as num from LoanBook group by BookId  ) end

[htl258_Tony]

create procedure SelectLendingList
@qty int
as
begin 
   select top (@qty) *,BookId,num from BookInfo where BookInfo.Id=BookId and BookId
   in(select BookId from LoanBook)
end

在这种情况下只需这样。

[lanytin]

好多错误……

[sdhdy]

--看看我的。
create procedure SelectLendingList
@qty int
as
begin 
exec('select top '+@qty+' * from 
(select a.bookid,b.name,count(1) num from LoanBook a,BookInfo b where a.bookid=b.id group by a.bookid,b.name) c
order by c.num desc,c.bookid,c.name')
end

[sdhdy]

--modify
create procedure SelectLendingList
@qty int
as
begin 
exec('select top '+@qty+' * from 
(select a.bookid,b.name,count(a.bookid) num from LoanBook a,BookInfo b where a.bookid=b.id group by a.bookid,b.name) c
order by c.num desc,c.bookid,c.name')
end

[lanytin]

请教一下Sdhyd:什么情况下需要将sql语句写出字符串的形式呢？
还是和直接那样执行没什么区别呢？

[sdhdy]

--以下情况必须写字符串格式。

1 :普通SQL语句可以用Exec执行 

Select * from tableName 
Exec('select * from tableName') 
Exec sp_executesql N'select * from tableName' -- 请注意字符串前一定要加N 

2:字段名，表名，数据库名之类作为变量时，必须用动态SQL 

declare @fname varchar(20) 
set @fname = 'FiledName' 
Select @fname from tableName -- 错误,不会提示错误，但结果为固定值FiledName,并非所要。 
Exec('select ' + @fname + ' from tableName') -- 请注意 加号前后的 单引号的边上加空格 

当然将字符串改成变量的形式也可 
declare @fname varchar(20) 
set @fname = 'FiledName' --设置字段名 

declare @s varchar(1000) 
set @s = 'select ' + @fname + ' from tableName' 
Exec(@s) -- 成功 
exec sp_executesql @s -- 此句会报错 

declare @s Nvarchar(1000) -- 注意此处改为nvarchar(1000) 
set @s = 'select ' + @fname + ' from tableName' 
Exec(@s) -- 成功 
exec sp_executesql @s -- 此句正确 

3. 输出参数 
declare @num int, 
@sqls nvarchar(4000) 
set @sqls='select count(*) from tableName' 
exec(@sqls) 

--如何将exec执行结果放入变量中？ 

declare @num int, @sqls nvarchar(4000) 
set @sqls='select @a=count(*) from tableName ' 
exec sp_executesql @sqls,N'@a int output',@num output 
select @num 

[claro]

每天都问，分能多给点么？

[lanytin]

[Quote=引用 9 楼 claro 的回复:]
每天都问，分能多给点么？
[/Quote]
月底有回馈感谢贴，散发哟！