DROP FUNCTION IF EXISTS fnF1
DROP FUNCTION IF EXISTS fnF2
GO
CREATE FUNCTION fnF1(@string varchar(max), @delimiter char(1))
RETURNs  @output  table (id int not null)
as
BEGIN
	
	IF CHARINDEX('|', @string) = 0
	begin
		INSERT @output (id)
		SELECT intSplit.Id 
			FROM fnF2(@string, @delimiter) AS intSplit
	END ELSE BEGIN
		INSERT @output (id)
		SELECT intSplit.Id 
			FROM string_split(@string, '|') svalue
				CROSS APPLY fnF2(svalue.value, @delimiter) AS intSplit
	END

	RETURN
END
GO
CREATE FUNCTION fnF2(@string varchar(max), @delimiter char(1))
RETURNs table
as
return
	select id 
	from fnF1(@string, @delimiter)
	WHERE CHARINDEX('|', @string) <> 0
	UNION ALL
	SELECT DISTINCT CAST(LTRIM(RTRIM(Value)) AS INT) as id
	FROM string_split(@string, @delimiter)
    WHERE len(LTRIM(RTRIM(Value)))>0
    AND CHARINDEX('|', @string) = 0

GO

SELECT * FROM fnF2('3',',')

declare @s varchar(max) = '3', @delimeter char(1) = ',';

select distinct
 b.value
from
 string_split(replace(@s, @delimeter, '|'), '|') a cross apply
 (select rtrim(ltrim(a.value))) b(value)
where
 b.value > '';

CREATE FUNCTION fnF2(@string varchar(max), @delimiter char(1))
RETURNs table
as
return
	select ss.id 
	from (select @string as string, CHARINDEX('|', data.string) as I) as data
               cross apply fnF1(data.string, @delimiter) as ss
	WHERE data.I <> 0
	UNION ALL
	SELECT DISTINCT CAST(LTRIM(RTRIM(Value)) AS INT) as id
	FROM string_split(@string, @delimiter)
    WHERE len(LTRIM(RTRIM(Value)))>0
    AND CHARINDEX('|', @string) = 0