demo, Sql Server - rextester

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CREATE FUNCTION dbo.[fnSplitString] 
( 
    @string NVARCHAR(MAX), 
    @delimiter CHAR(1) 
) 
RETURNS @output TABLE(splitdata NVARCHAR(MAX) 
) 
BEGIN 
    DECLARE @start INT, @end INT 
    SELECT @start = 1, @end = CHARINDEX(@delimiter, @string) 
    WHILE @start < LEN(@string) + 1 BEGIN 
        IF @end = 0  
            SET @end = LEN(@string) + 1
       
        INSERT INTO @output (splitdata)  
        VALUES(SUBSTRING(@string, @start, @end - @start)) 
        SET @start = @end + 1 
        SET @end = CHARINDEX(@delimiter, @string, @start)
        
    END 
    RETURN 
END

-- select * from dbo.fnSplitString('123.45.678', '.');

create table test (id int, col1 varchar(100), col2 varchar(100), col3 varchar(100), col4 varchar(100));

insert test values (1, '/txt1/txt2', null, null, null),
(2, null, '/txt1/txt4', null, null),
(3, null, '/txt2/txt3', null, null),
(4, null, '/txt4', null, '/txt5/txt6');

select t.id, x.splitdata from test t cross apply dbo.fnSplitString(coalesce(col1, '') + coalesce(col2, '') + coalesce(col3, '') + coalesce(col4, ''), '/') x
where coalesce(x.splitdata, '') <> ''

View schema
Execution time: 0,02 sec, rows selected: 9, rows affected: 4, absolute service time: 0,17 sec