How to group (case) statements results or concatenate one of them?

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Oracle

Hello,

How can I concatenate all of

CACSE(...)

result rows into into one?
Additionaly - is there a way to group multiple statements without "MAX" added into single entry?

Please check lines below, I might have been mistaken with part of it:

select				
max(case when source_column_a in (value_1) then value else null) as "value_a",				
(case when source_column_a in (value_2) then value else null) as "value_b",				
(case when source_column_a in (value_3) then value else null) as "value_c",				
max(case when source_column_a in (value_4) then value else null) as "value_d"				
from table				
group by ID, (case when source_column_a in (value_2) then value else null), (case when source_column_a in (value_3) then value else null);				
				
				
example result:				
	value_a	value_b	value_c	value_d
	Amax	(null)	(null)	Dmax
	(null)	B1	    (null)	(null)
	(null)	B2	    (null)	(null)
	(null)	B3	    (null)	(null)
	(null)	Bmax	(null)	(null)
	(null)	(null)	C1	    (null)
	(null)	(null)	C2	    (null)
	(null)	(null)	C3	    (null)
	(null)	(null)	Cmax	(null)
				
				
Results to achieve:				
	value_a	value_b	value_c	value_d
	Amax	Bmax	CMax	Dmax
	(null)	B3	    C3	    (null)
	(null)	B2	    C2	    (null)
	(null)	B1	    C1	    (null)
				
	value_a	value_b	value_c	value_d
	Amax	Bmax, B3, B2, B1	Cmax, C3, C2, C1	Dmax

Regards,

What I have tried:

In situation related to additional one - query might have been modified more than once to include at least one of the cases in group by.