Microsoft SQL Server 2016 (SP2-CU6) (KB4488536) - 13.0.5292.0 (X64) 
	Mar 11 2019 23:19:30 
	Copyright (c) Microsoft Corporation
	Developer Edition (64-bit) on Windows Server 2016 Standard 10.0 <X64> (Build 14393: ) (Hypervisor)

drop table if exists myTable
GO
CREATE TABLE [dbo].[myTable](
	[myChar2] [char](2) NOT NULL,
	[myId] [int] NOT NULL,
	[myFk] [int] NOT NULL,
	[myDayId] [int] NOT NULL,
	[sbor_1] [numeric](16, 2) NOT NULL,
	[sbor_2] [numeric](16, 2) NOT NULL,
	[sbor_3] [numeric](16, 2) NOT NULL,
 CONSTRAINT [PK_myTable] PRIMARY KEY CLUSTERED 
(
	[myDayId] ASC,
	[myId] ASC,
	[myFk] ASC,
	[myChar2] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO

CREATE  or alter FUNCTION [dbo].myFunc(
	  @name		varchar(256)	
	  ,@value	sql_variant
)
returns varchar(8000)
as
begin
	return ',' + @name
end
GO

-- заполняем 1000 записями: [myId] от 1 до 500, по двум [myDayId]
;with cteDay([myDayId]) as(select 1 union select 2)
	,cte([myFk],[myChar2]) as (select 1,'aa')
	,cte1_5(i) as (  select 0 union select 1 union select 2 union select 3 union select 4)
	, cte_id([myId]) as (select 1
							union all
							select [myId]+1 from cte_id
							where [myId] < 100
						)
insert [myTable]
select [myChar2], [myId]+i*100, [myFk], [myDayId], 1,1,1
	from cteDay
	cross join cte
	cross join cte_id
	cross join cte1_5 
order by 2
	;

declare @reply varchar(max) = ''
             ,@reply2 varchar(max) = ''

select @reply += [dbo].myFunc([myId],[myId])
  --, @reply2 += [dbo].myFunc(sbor_type,[myId])
    from
    (    select
             [myTable].[myId]
            , sbor_1    = sum(sbor_1)
            , sbor_2    = sum(sbor_2)
            , sbor_3    = sum(sbor_3)
         from
            [myTable]
        group by [myId]
    ) sbor
          unpivot (
            sbor_sum for sbor_type in (
                  sbor_1
                , sbor_2
                , sbor_3
                )
            ) as unpv
    order by
          sbor_type,
         [myId]
    option (recompile)

print( @reply)
print( @reply2)