Microsoft sql select distinct certain columns - sql-server

Question

I am changing mysql queries to microsoft sql server 2008 queries, and in order to apply limit I need to select a ROW_NUMBER() that accumlates over each row and then apply a where condition WHERE RowNum >= 0 AND RowNum < 0 + 20 to select a certain limit with offset.
My issue however is that I can no longer select distinct because I have a column RowNum that is different with each row, here's my query:
USE mydatabase
GO
WITH Results_CTE
AS (
SELECT DISTINCT C.firstname
,C.lastname
,C.id AS clientid
,QC.category_name
,QR.id
,QR.cid
,QR.catid
,QR.rhid
,ROW_NUMBER() OVER (
ORDER BY QR.id DESC
) AS RowNum
FROM cms_question_report QR
,cms_clients C
,cms_questioncategory QC
WHERE C.id = QR.cid
AND QR.catid = '3'
AND QR.catid = QC.id
)
SELECT *
FROM Results_CTE
WHERE RowNum >= 0
AND RowNum < 0 + 20
And the results are:
╔═══════════╦══════════╦══════════╦═══════════════╦═══════╦═════╦═══════╦══════╦════════╗
║ firstname ║ lastname ║ clientid ║ category_name ║ id ║ cid ║ catid ║ rhid ║ RowNum ║
╠═══════════╬══════════╬══════════╬═══════════════╬═══════╬═════╬═══════╬══════╬════════╣
║ test ║ testing ║ 121 ║ Activity Log ║ 81499 ║ 121 ║ 3 ║ 0 ║ 19 ║
║ test ║ testing ║ 121 ║ Activity Log ║ 81498 ║ 121 ║ 3 ║ 0 ║ 20 ║
║ test ║ testing ║ 121 ║ Activity Log ║ 81497 ║ 121 ║ 3 ║ 0 ║ 21 ║
║ test ║ test ║ 120 ║ Activity Log ║ 81496 ║ 120 ║ 3 ║ 0 ║ 22 ║
║ test ║ test ║ 120 ║ Activity Log ║ 81495 ║ 120 ║ 3 ║ 0 ║ 23 ║
║ test ║ test ║ 120 ║ Activity Log ║ 81494 ║ 120 ║ 3 ║ 0 ║ 24 ║
║ test ║ test ║ 120 ║ Activity Log ║ 81493 ║ 120 ║ 3 ║ 0 ║ 25 ║
╚═══════════╩══════════╩══════════╩═══════════════╩═══════╩═════╩═══════╩══════╩════════╝
I took an example from the middle of the result. What I'm after is for example:
╔═══════════╦══════════╦══════════╦═══════════════╦═══════╦═════╦═══════╦══════╦════════╗
║ firstname ║ lastname ║ clientid ║ category_name ║ id ║ cid ║ catid ║ rhid ║ RowNum ║
╠═══════════╬══════════╬══════════╬═══════════════╬═══════╬═════╬═══════╬══════╬════════╣
║ test ║ testing ║ 121 ║ Activity Log ║ 81497 ║ 121 ║ 3 ║ 0 ║ 21 ║
║ test ║ test ║ 120 ║ Activity Log ║ 81496 ║ 120 ║ 3 ║ 0 ║ 22 ║
╚═══════════╩══════════╩══════════╩═══════════════╩═══════╩═════╩═══════╩══════╩════════╝
Where I am trying to group the results by clientid. How do I achieve that?

Answer 1

USE ctarspla_mercycs
GO
WITH Results_CTE AS
(SELECT *, ROW_NUMBER() OVER (ORDER BY CLIENTID DESC) AS RowNum
FROM (SELECT DISTINCT
C.firstname,
C.lastname,
C.id as clientid,
QC.category_name,
QR.catid,
QR.rhid
FROM
cms_question_report QR,
cms_clients C,
cms_questioncategory QC
WHERE C.id=QR.cid
AND QR.catid=3
AND QR.catid=QC.id) t1)
SELECT * FROM Results_CTE
WHERE RowNum >= 0
AND RowNum < 0 + 20