SQL select动态记录数

Question

使用SQL Server2005，我试图根据另一个表从一个表中选择一定数量的记录(动态)，以获得需要的记录数量。

表1有一个category ID和我希望为该类别返回的记录数。

Category ID  TOP_Limit
----------------------  
Cat 1        1
Cat 2        2
Cat 3        10

表2包含产品ID、类别ID和数量：

Product ID  Category ID  Quantity
---------------------------------
Part 1      Cat 1        10  
Part 2      Cat 1        20  
Part 3      Cat 2        100  
Part 4      Cat 2        100  
Part 5      Cat 2        50  
Part 6      Cat 3        5  

我如何编写一个查询来从表2 (第2部分，第3& 4部分，第6部分)中获得正确的“顶级”产品记录？

Answer 1

尝试如下所示：

;with cte as (
  select ProductID, CategoryID, Quantity,
         [row] = row_number() over(partition by CategoryID order by Quantity desc)
  from Table2
)
select t2.Product, t2.CategoryID, t2.Quantity
from cte t2
     join Table1 t1 on t2.CategoryID=t1.CategoryID
where t2.row <= t1.TOP_Limit

Answer 2

我想这样就行了。

declare @Table1 table (
    Cat int,
    TOP_Limit int
)

declare @Table2 table (
    Part int,
    Cat int,
    Quantity int
)

insert into @Table1
    (Cat, TOP_Limit)
    select 1,1 union all
    select 2,2 union all
    select 3,10

insert into @Table2
    (Part, Cat, Quantity)
    select 2,1,20 union all
    select 3,2,100 union all
    select 4,2,100 union all
    select 5,2,50 union all
    select 6,3,5

;with cteRowNums as (
    select t2.Part, t2.Cat, t2.Quantity, 
           ROW_NUMBER() over(partition by t2.Cat order by t2.Quantity desc, t2.Part) as rownum
        from @Table2 t2
            inner join @Table1 t1
                on t2.Cat = t1.Cat
)
select c.Part, c.Cat, c.Quantity
    from cteRowNums c           
        inner join @Table1 t1
            on c.Cat = t1.Cat
                and c.rownum <= t1.TOP_Limit