SQL select dynamic number of records

Question

Using SQL Server 2005, I am trying to select a certain number of records (dynamic) from one table, based on another table to get what that number of records needs to be.

Table 1 has a Category ID and the number of records I want returned for that category.

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

Table 2 has a Product ID, the Category ID, and a Quantity:

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  

How can I write a query that will get me the correct "top" product records from Table 2 (Part 2, Part 3 & 4, Part 6)?

Answer 1

Try something like this:

;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

I think this will do it.

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