这是我在这里重复这个问题时给出的答案：

/* Set up test data */
create table Folders (
    FolderID int,
    FolderName varchar(10),
    ParentID int
)

insert into Folders
    (FolderID, FolderName, ParentID)
    select 1,'Folder1',0 union all
    select 2,'Folder2',1 union all
    select 3,'Folder3',2 union all
    select 4,'Folder4',3        
go

/* Create function */
create function dbo.CreateFolderPath (@FolderID int)
returns varchar(1000)
as
begin
    declare @ParentID int
    declare @FolderPath varchar(1000)
    set @FolderPath = ''

    select @ParentID = ParentID
        from Folders
        where FolderID = @FolderID

    while @ParentID<>0 begin
        select @FolderPath = FolderName + '\' + @FolderPath, @ParentID = ParentID
            from Folders
            where FolderID = @ParentID
    end /* while */

    return @FolderPath
end /* function */
go

/* Demo the function */
select dbo.CreateFolderPath(4)

/* Clean up after demo */
drop function dbo.CreateFolderPath
drop table Folders