Dynamic Cols Pivot Rows but only some columns, not all - sql

Question

I'm making a dynamic pivot table with a similar structure in the example below.
Query to list each child record in columns of a parent
EXCEPT, all the examples I seem to find, when building the list of dynamics columns for the pivot, they all use "quotename" to get all columns in the table, while I only want a handful for my output.
select #colsPivot = STUFF((SELECT ','
+ quotename(c.name +'_'+ cast(t.rn as varchar(10)))
from
(
select cast(row_number() over(partition by m.MemberID order by g.guestid) as varchar(50)) rn
from member m
left join guest g
on m.guestid = g.guestid
) t
cross apply sys.columns as C
where C.object_id = object_id('guest')
group by c.name, t.rn
order by t.rn
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
Wondering if anyone can help with the syntax. In the above example, instead of getting First name and Last Name, hypothetically, I only want Last Name. How would that look?
I'm just looking at how to replace the quotename properly, I believe I have the rest running properly.
SAMPLE:
Member Table
MemberID | FName | LName
001 Frank Smith
002 Mary Jane
003 John Henry
Guest Table
GuestID | FName | LName | MemberId
101 Steve Smith | 001
102 Peter Smith | 001
103 Mike Jane | 002
OUTPUT:
MemberID | FName | LName| GuestID1 | LName1 |GuestID2 | LName2
001 Frank Smith 101 Smith 102 Smith
002 Mary Jane 103 Jane
003 John Henry
Any and all help is much appreciated!

Answer 1

Key point is that we need to use row_number window function to make a row number and then use condition aggregate function to make it.
SELECT MemberID,FName,LName,
MAX(CASE WHEN rn = 1 THEN GuestID END) GuestID1,
MAX(CASE WHEN rn = 1 THEN g_LName END) LName1,
MAX(CASE WHEN rn = 2 THEN GuestID END) GuestID2,
MAX(CASE WHEN rn = 2 THEN g_LName END) LName2
FROM (
SELECT m.MemberID,
m.FName,
m.LName,
GuestID,
g.LName g_LName,
ROW_NUMBER() OVER(PARTITION BY m.MemberID ORDER BY GuestID) rn
FROM Member m LEFT JOIN Guest g
ON m.MemberId = g.MemberId
) t1
GROUP BY MemberID,FName,LName
if there might be multiple LName (more than 2) and you want to use Dynamic pivot you can try the below code, but that might be a little complex.
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX);
SET #cols = STUFF((
SELECT distinct ', MAX(CASE WHEN rn = '+ CAST(t1.cnt AS VARCHAR(5)) + ' THEN GuestID END)' + ' as '''+CONCAT(name,t1.cnt)+''''
FROM (SELECT COUNT(*) cnt FROM Guest GROUP BY MemberId) t1
CROSS JOIN (SELECT 'GuestID' name UNION ALL SELECT 'LName') t2
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT MemberID,FName,LName, ' + #cols + '
FROM (
SELECT m.MemberID,
m.FName,
m.LName,
GuestID,
g.LName g_LName,
ROW_NUMBER() OVER(PARTITION BY m.MemberID ORDER BY GuestID) rn
FROM Member m LEFT JOIN Guest g
ON m.MemberId = g.MemberId
) t1
GROUP BY MemberID,FName,LName '
execute(#query)
sqlfiddle