SQL Server recursive CTE and paging - sql-server

Question

I have this table
CREATE TABLE [dbo].[friend_blocked_list](
[subdomain] [varchar](50) NOT NULL,
[un] [nvarchar](50) NOT NULL,
[friend] [nvarchar](50) NOT NULL,
[is_blocked] [bit] NOT NULL,
[approved] [bit] NOT NULL)
where i select data from it with below query. Select query combines users that added user as friend and users that have been added as friend by user
declare #un varchar(50), #subdomain varchar(50)
set #un='user2';
set #subdomain ='test.domain.com';
WITH FRIENDS as
(
SELECT friend
FROM friend_blocked_list
WHERE un=#un and subdomain=#subdomain and approved=1 and is_blocked=0
UNION ALL
SELECT un as friend
FROM friend_blocked_list
WHERE friend=#un and subdomain=#subdomain and approved=1 and is_blocked=0
)
select friend from FRIENDS group by FRIENDS.friend order by FRIENDS.friend asc
It works fine with small amout of data but i want to be able to do a paging on the server side in order to reduce load. I am trying to combine it with my paging sp below
create PROCEDURE [dbo].[Paging]
#subdomain varchar(50),
#un varchar(50),
#PageNumber int,
#PageSize int
AS
BEGIN
--paging
DECLARE #FirstRow INT,#LastRow INT,#RowCount INT,#PageCount INT
--find recordcount and pages
SELECT #RowCount = COUNT(*), #PageCount = COUNT(*) / #PageSize
FROM friend_blocked_list
WHERE subdomain=#subdomain AND un=#un AND approved=1 AND is_blocked=0;
--- calculate pages
IF #RowCount % #PageSize != 0 SET #PageCount = #PageCount + 1
IF #PageNumber < 1 SET #PageNumber = 1
IF #PageNumber > #PageCount SET #PageNumber = #PageCount
SELECT
CurrentPage = #PageNumber,
TotalPages = #PageCount,
TotalRows = #RowCount
-- mora calculation
SELECT #FirstRow = ( #PageNumber - 1) * #PageSize + 1,
#LastRow = (#PageNumber - 1) * #PageSize + #PageSize ;
WITH MyTopics AS
(
SELECT *, ROW_NUMBER() OVER (order by un asc) AS RowNumber
FROM friend_blocked_list
WHERE subdomain=#subdomain AND un=#un AND approved=1 AND is_blocked=0
)
SELECT *
FROM MyTopics
WHERE RowNumber BETWEEN #FirstRow AND #LastRow
ORDER BY RowNumber ASC;
end
But as always i am having trouble :). Main problem is the UNION ALL in my query. It prevents me using ROW_NUMBER() OVER.
Any ideas?

Answer 1

Here's your procedure updated for paging:
CREATE PROCEDURE [dbo].[Paging]
#subdomain varchar(50),
#un varchar(50),
#PageNumber int,
#PageSize int
AS
DECLARE #start_row int
DECLARE #end_row int
SET #end_row = #PageNumber * #PageSize
SET #start_row = #end_row - (#PageSize - 1)
BEGIN
WITH FRIENDS AS (
SELECT t.friend
FROM FRIEND_BLOCKED_LIST t
WHERE t.un = #un
AND t.subdomain = #subdomain
AND t.approved = 1
AND t.is_blocked = 0
UNION ALL
SELECT t.un as friend
FROM FRIEND_BLOCKED_LIST t
WHERE t.friend = #un
AND t.subdomain = #subdomain
AND t.approved = 1
AND t.is_blocked = 0)
SELECT t.friend
FROM (SELECT f.friend,
ROW_NUMBER() OVER (ORDER BY f.friend) AS rownum
FROM FRIENDS f
GROUP BY f.friend) t
WHERE t.rownum BETWEEN #start_row AND #end_row
END
It might be possible to change the query to use one CTE if you could provide more information on the FRIEND_BLOCKED_LIST table. The UNION of two queries with identical WHERE clauses while differentiating between two columns makes me wonder if it couldn't be written better. Could the FRIENDS CTE be rewritten as:
SELECT COALESCE(t.un, t.friend) as friend
FROM FRIEND_BLOCKED_LIST t
WHERE #un = COALESCE(t.un, t.friend)
AND t.subdomain = #subdomain
AND t.approved = 1
AND t.is_blocked = 0

Answer 2

Apply the row number to the list you want to return:
WITH FRIENDS as
(
SELECT friend
FROM friend_blocked_list
WHERE un=#un and subdomain=#subdomain and approved=1 and is_blocked=0
UNION ALL
SELECT un as friend
FROM friend_blocked_list
WHERE friend=#un and subdomain=#subdomain and approved=1 and is_blocked=0 )
, recursive_friends as (
select friend
, row_number() over (order by friend asc) as rn
from FRIENDS )
select friend
from recursive_friends
where rn between #firstRow and #lastRow
order by FRIENDS.friend asc;