Pagination and INNER JOIN

Question

I have a situation which I need to do pagination along with INNET JOIN. Here is a similar scenario I have:

DECLARE @categories AS TABLE(
    CatID INT,
    CategoryName NVARCHAR(100)
);

DECLARE @fooTable AS TABLE(
    ID INT,
    CatID INT,
    Name NVARCHAR(100),
    MinAllow INT,
    Price DECIMAL(18,2)
);

INSERT INTO @categories  VALUES(1, 'Cat1');
INSERT INTO @categories  VALUES(2, 'Cat2');
INSERT INTO @categories  VALUES(3, 'Cat3');
INSERT INTO @categories  VALUES(4, 'Cat4');
INSERT INTO @categories  VALUES(5, 'Cat5');

INSERT INTO @fooTable  VALUES(1, 1, 'Product1', 2, 112.2);
INSERT INTO @fooTable  VALUES(3, 1, 'Product3', 5, 233.32);
INSERT INTO @fooTable  VALUES(6, 1, 'Product6', 4, 12.43);
INSERT INTO @fooTable  VALUES(7, 4, 'Product7', 4, 12.43);
INSERT INTO @fooTable  VALUES(8, 5, 'Product8', 4, 12.43);

These are the records I have. As you can see, some categories do not have any products inside @fooTable. As a next step, we have the following SELECT statement:

SELECT * FROM @fooTable ft
INNER JOIN (
    SELECT ROW_NUMBER() OVER (ORDER BY CatID) AS RowNum, * FROM @categories
) AS cat ON (cat.CatID = ft.CatID);

It is a basic JOIN except that the output will also carry the row number of the categories. The result I got for this query is as follows:

ID   CatID   Name          MinAllow    Price     RowNum   CatID    CategoryName
---- ------- ------------- ----------- --------- -------- -------- -------------
1    1       Product1      2           112.20    1        1        Cat1
3    1       Product3      5           233.32    1        1        Cat1
6    1       Product6      4           12.43     1        1        Cat1
7    4       Product7      4           12.43     4        4        Cat4
8    5       Product8      4           12.43     5        5        Cat5

When you look at the RowNum column, you will see that those values are not pagination friendly. So, when I try to paginate this table as follows, I got an incorrect output:

SELECT * FROM @fooTable ft
INNER JOIN (
    SELECT ROW_NUMBER() OVER (ORDER BY CatID) AS RowNum, * FROM @categories
)AS cat ON (cat.CatID = ft.CatID) AND (cat.RowNum BETWEEN 1 AND 2);

The real situation I have is similar to this one but that query is so complicated and I need to get it working with INNER JOIN. I hope I made it clear. Any idea how I got something like that working?

Edit

According to the above result of my first select query, I should be able to retrieve products whose CatID is 1 and 4 on my second query. That's what I aim.

Answer 1

One solution can be the next one:

SELECT  x.*
FROM
(
        SELECT  ft.*, 
                cat.CategoryName,
                DENSE_RANK() OVER (ORDER BY ft.CatID) AS Rnk
        FROM @fooTable ft
        INNER JOIN @categories cat ON (cat.CatID = ft.CatID)
) AS x
WHERE   x.Rnk BETWEEN 1 AND 2

Results:

ID CatID Name     MinAllow Price   CategoryName Rnk
-- ----- -------- -------- ------- ------------ ---
1  1     Product1 2        112.20  Cat1         1
3  1     Product3 5        233.32  Cat1         1
6  1     Product6 4        12.43   Cat1         1
7  4     Product7 4        12.43   Cat4         2