How to use ROW_NUMBER in the following procedure? - tsql

Question

I have the following stored procedure which returns A, B, and the count in descending order. I am trying to use ROW_NUMBER, so I can page the records, but I want the first row number 1 to be the record with the highest count, so basically, if I return a table with 3 records and the count is 30, 20, 10, then row number 1 should correspond with count 30, row number 2 should correspond with count 20, and row number 3 should correspond with count 10. dbo.f_GetCount is a function that returns a count.
create procedure dbo.Test
as
#A nvarchar(300) = NULL,
#B nvarchar(10) = NULL
as
select #A = nullif(#A,'')
,#B = nullif(#B,'');
select h.A
,hrl.B
,dbo.f_GetCount(hrl.A,h.B) as cnt
from dbo.hrl
inner join dbo.h
on h.C = hrl.C
where(#A is null
or h.A like '%'+#A+'%'
)
and (#B is null
or hrl.B = #B
)
group by hrl.B
,h.A
order by cnt desc;

Answer 1

WITH q AS
(
SELECT h.A, hrl.B,
dbo.f_GetCount(hrl.A,h.B) as cnt
FROM dbo.hrl
INNER JOIN dbo.h on h.C = hrl.C
WHERE (#A IS NULL OR h.A like '%' + #A + '%')
AND (#B IS NULL OR hrl.B = #B)
GROUP BY hrl.B, h.A
)
SELECT q.*, ROW_NUMBER() OVER (ORDER BY cnt DESC) AS rn
FROM q
ORDER BY rn DESC
To retrieve first 10 rows, use:
WITH q AS
(
SELECT h.A, hrl.B,
dbo.f_GetCount(hrl.A,h.B) as cnt
FROM dbo.hrl
INNER JOIN dbo.h on h.C = hrl.C
WHERE (#A IS NULL OR h.A like '%' + #A + '%')
AND (#B IS NULL OR hrl.B = #B)
GROUP BY hrl.B, h.A
)
SELECT TOP 10 q.*,
ROW_NUMBER() OVER (ORDER BY cnt DESC, A, B) AS rn
FROM q
ORDER BY cnt DESC, A, B
To retrieve rows between 11 and 20, use:
SELECT *
FROM (
WITH q AS
(
SELECT h.A, hrl.B,
dbo.f_GetCount(hrl.A,h.B) as cnt
FROM dbo.hrl
INNER JOIN dbo.h on h.C = hrl.C
WHERE (#A IS NULL OR h.A like '%' + #A + '%')
AND (#B IS NULL OR hrl.B = #B)
GROUP BY hrl.B, h.A
)
SELECT q.*,
ROW_NUMBER() OVER (ORDER BY cnt DESC, A, B) AS rn
FROM q
) qq
WHERE rn BETWEEN 11 AND 20
ORDER BY cnt DESC, A, B

Answer 2

I would use a sub-query to get the values of the function into the result, and then the ROW_NUMBER ranking function, like so:
select
ROW_NUMBER() over (order by t.cnt desc) as RowId, t.*
from
(
SELECT
h.A, hrl.B, dbo.f_GetCount(hrl.A,h.B) as cnt
FROM
dbo.hrl
INNER JOIN dbo.h on h.C = hrl.C
WHERE
(#A IS NULL OR h.A like '%' + #A + '%') AND
(#B IS NULL OR hrl.B = #B)
GROUP BY
hrl.B, h.A
) as t
order by
1
If you wanted only a certain section of results (say, for paging), then you would need another subquery, and then filter on the row number:
select
t.*
from
(
select
ROW_NUMBER() over (order by t.cnt desc) as RowId, t.*
from
(
SELECT
h.A, hrl.B, dbo.f_GetCount(hrl.A,h.B) as cnt
FROM
dbo.hrl
INNER JOIN dbo.h on h.C = hrl.C
WHERE
(#A IS NULL OR h.A like '%' + #A + '%') AND
(#B IS NULL OR hrl.B = #B)
GROUP BY
hrl.B, h.A
) as t
) as t
where
t.RowId between 1 and 10
order by
t.RowId
Note that in this query, you could put ROW_NUMBER anywhere in the select list, since you are no longer reliant on using the "order by 1" syntax for the order by statement.
There is a subtle issue here when calling this query multiple times. It is not guaranteed that the order in which the records are returned are going to be consistent if the number of items in each group is not unique. In order to address this, you have to change the ROW_NUMBER function to order on the fields that make up the group in the count.
In this case, it would be A and B, resulting in:
select
t.*
from
(
select
ROW_NUMBER() over (order by t.cnt desc, t.A, t.B) as RowId, t.*
from
(
SELECT
h.A, hrl.B, dbo.f_GetCount(hrl.A,h.B) as cnt
FROM
dbo.hrl
INNER JOIN dbo.h on h.C = hrl.C
WHERE
(#A IS NULL OR h.A like '%' + #A + '%') AND
(#B IS NULL OR hrl.B = #B)
GROUP BY
hrl.B, h.A
) as t
) as t
where
t.RowId between 1 and 10
order by
t.RowId
This ends up ordering the results consistently between calls when the count of the items between groups is not unique (assuming the same set of data).

Answer 3

SELECT h.A, hrl.B,
dbo.f_GetCount(hrl.A,h.B) as cnt,
ROW_NUMBER() over (order by cnt desc) as row_num
FROM dbo.hrl
INNER JOIN dbo.h on h.C = hrl.C
WHERE (#A IS NULL OR h.A like '%' + #A + '%')
AND (#B IS NULL OR hrl.B = #B)
GROUP BY hrl.B, h.A
ORDER BY cnt desc
This should do the trick. I don't have SSMS in front of me to test, but you MAY have to substitute the usage of 'cnt' in the ROW_NUMBER's order by clause with a second call to the function, but this should give you the general idea.