Paginating a parent in SQL Server on a parent/child query - sql-server

Question

(SQL Server 2012 - Web Edition)
I have a parent/child (one to many) relationship in a query like so:
SELECT a.a, a.b, b.c
FROM tablea INNER JOIN
tableb ON b.pk = a.fk
I have a huge pagination query that encompasses this using the standard (psuedo-code):
WITH C as (SELECT top(#perpage*#pagenum) rowID = row_number() OVER (somefield)),
SELECT c.* FROM C (query) WHERE DT_RowId > (#pagenum-1)*#perpage
The question I have is in this scenario is it possible to paginate off the parent table (a), instead of the entire query? Can I modify my pagination query (not the sql that pulls the query itself) so that when I ask for 10 rows, it gives me 10 rows from the parent, with 'x' number of children attached?
I know I'm not giving the bigger picture here, but the bigger picture is ugly. If need be, we can go there, but it's out there. Here's a small taste of where we're going with this:
IF UPPER(LEFT(#rSQL, 6)) = 'SELECT'
BEGIN
SET #rSQL = 'SELECT * FROM (' + #rSQL + ')' + ' as rTBL';
SET #rSQL = RIGHT(#rSQL, LEN(#rSQL)-7);
IF (LEN(LTRIM(#search)) > 0)
BEGIN
SET #rPaging =
'IF (#schemaonly=1) SET FMTONLY ON;
SELECT #ttlrows = COUNT(*) FROM (SELECT ' + #rSQL + #rWhere + ') AS TBL;
WITH C as (select top(#perpage*#pagenum) DT_RowId = ROW_NUMBER() OVER (' + #rOrder + '), ';
SET #rPaging = #rPaging + #rSQL + #rWhere + ')
SELECT C.*' + #rcols + ', (#perpage-1) * #pagenum as pagenum, #ttlrows as ct, CEILING(#ttlrows / CAST(#perpage AS FLOAT)) as pages
FROM C '+ #query + ' WHERE DT_RowId > (#pagenum-1) * #perpage ';
END
ELSE
BEGIN
SET #rPaging =
'IF (#schemaonly=1) SET FMTONLY ON;
SELECT #ttlrows = COUNT(*) FROM (' + #oSQL + ') AS SUBQUERY;
WITH C as (select top(#perpage*#pagenum) DT_RowId = ROW_NUMBER() OVER (' + #rOrder + '), ';
SET #rPaging = #rPaging + #rSQL + ')
SELECT C.*' + #rcols + ',(#perpage-1) * #pagenum as pagenum, #ttlrows as ct, CEILING(#ttlrows / CAST(#perpage AS FLOAT)) as pages
FROM C '+ #query + ' WHERE DT_RowId > (#pagenum-1) * #perpage ';
END
PRINT #rPaging;
EXECUTE SP_EXECUTESQL #rPaging, #parms, #ttlrows out, #schemaonly, #perpage, #pagenum, #fksiteID, #filter1, #filter2, #filter3, #filter4, #intfilter1, #intfilter2, #intfilter3, #intfilter4, #datefilter1, #datefilter2, #search;
SET FMTONLY OFF;
END
ELSE
BEGIN
SET #rSQL = LTRIM(REPLACE(UPPER(#rSQL), 'EXEC',''));
EXECUTE SP_EXECUTESQL #rSQL, #parms, #ttlrows out, #schemaonly, #perpage, #pagenum, #fksiteID, #filter1, #filter2, #filter3, #filter4, #intfilter1, #intfilter2, #intfilter3, #intfilter4, #datefilter1, #datefilter2;
END

Answer 1

You could do the pagination in a CTE that only gets the parent rows, and then join the child rows in a subsequent CTE or in the main query.
Due to the dynamic way you are using this, this might have to involve building your pagination query from the same building blocks you use to build #query. Without seeing the code that builds #query I can't be much more specific than that.

Answer 2

You could add
,DENSE_RANK() OVER (ORDER BY table_a.primary_key)
This would indirectly provide the same result as
,ROW_NUMBER() OVER(ORDER BY table_a.primary_key)
but the former would be on the final result set instead going back to table a for the latter code snippet.
But please be aware of the disadvantage: any additional ranking function will force an additional sort operation on the result set! This might significantly influence the query performance. If this is the case in your scenario, I'd recommend to follow Tab Allemans solution and use a cte.