Ordering by a non-numeric hierarchy string numerically

I have a table with data representing a tree structure, with one column indicating the row's position in the hierarchical tree. Each level is separated with a -.

1
1-1
2
2-1
2-2
2-2-1
2-2-2
2-2-2-1

The tree is retrieved in order simply with an ORDER BY on this column. This falls down when there ar开发者_如何学编程e more than 10 items at any level, as the column is sorted alphabetically. MySQL sorts 10 before 3.

Actual result:

1
1-10
1-3
2

Desired result:

1
1-3
1-10
2

There could be any number of levels of depth to the values.

Is it possible to sort this data numerically in MySQL?

I think your best shot is to convert the data into something that does naturally sort. If you tree structure will always have less than 99 children, you could create a function like I have below. You would just use the "GetTreeStructureSort(columnName)" in the sort function. (If you have the possibility of 3-digit numbers, you could adjust this to be more intuitive.)

CREATE FUNCTION GetTreeStructureSort
(
    -- Add the parameters for the function here
    @structure varchar(500) 
)
RETURNS varchar(500)
AS
BEGIN

    DECLARE @sort varchar(500)

    -- Add a hyphen to the beginning and end to make all the numbers from 1 to 9 easily replaceable
    SET @sort = '-' + @structure + '-'

    -- Replace each instance of a one-digit number to a two-digit representation
    SELECT @sort = REPLACE(@sort, '-1-', '-01-')
    SELECT @sort = REPLACE(@sort, '-2-', '-02-')
    SELECT @sort = REPLACE(@sort, '-3-', '-03-')
    SELECT @sort = REPLACE(@sort, '-4-', '-04-')
    SELECT @sort = REPLACE(@sort, '-5-', '-05-')
    SELECT @sort = REPLACE(@sort, '-6-', '-06-')
    SELECT @sort = REPLACE(@sort, '-7-', '-07-')
    SELECT @sort = REPLACE(@sort, '-8-', '-08-')
    SELECT @sort = REPLACE(@sort, '-9-', '-09-')

    -- Strip off the first and last hyphens that were added at the beginning.
    SELECT @sort = SUBSTRING(@sort, 2, LEN(@sort) - 2)

    -- Return the result of the function
    RETURN @sort

END

This would convert these results:

1
1-10
1-3
2

into this:

01
01-03
01-10
02

I tested this with the following code:

DECLARE  @something varchar(255)
set @something = '1-10-3-21'

SELECT dbo.GetTreeStructureSort(@something)