T-SQL script that removes all non-digit characters from a string and normalizes digits from various Unicode ranges (Arabic-Indic, Persian, Fullwidth, etc.) to ASCII 0–9. Works for NVARCHAR strings of any length using a tally table.

digits_only.sql

---------------
-- Test Data --
---------------

declare @data table (v nvarchar(100));

insert into @data values
	  ('1234567890'), -- clean data
	  ('12345-67890'), -- middle non-digit character
	  ('12345 67890'),
	  ('12345x67890'),
	  ('12345ax 67890'), -- middle string 	  
	  ('  1234567890'), -- leading spaces
	  ('1234567890  '), -- trailing spaces
	  ('  1234567890  '), -- leading & trailing spaces
	  (' '), -- single space string
	  (''), -- empty string
	  (null),
	  (N'۱۲۳۴۵۶۷۸۹۰abc'),  -- Persian digits + Latin
	  (N'١٢٣٤٥٦٧٨٩٠ 漢字'),  -- Arabic-Indic digits + Chinese
	  (N'１２３４５６７８９０漢字');  -- Fullwidth digits + Chinese

-----------------------------------------------------------------------
-- Removes non-digit characters and normalizes digits to ASCII [0-9] --
-----------------------------------------------------------------------

;with numbers as (
    select number + 1 as n
    from master..spt_values
    where type = 'P' and number < 1000  -- this number has to be equal or more than max string length
)
select v,
       (
           select 
               case 
                   when u between 48 and 57 then nchar(u)
                   when u between 1632 and 1641 then nchar(u - 1632 + 48)
                   when u between 1776 and 1785 then nchar(u - 1776 + 48)
                   when u between 65296 and 65305 then nchar(u - 65296 + 48)
                   else null
               end
           from (
               select unicode(substring(isnull(v,''), n, 1)) as u, n
               from numbers
               where n <= len(isnull(v,''))
           ) as chars
           where u between 48 and 57
              or u between 1632 and 1641
              or u between 1776 and 1785
              or u between 65296 and 65305
           order by n
           for xml path(''), type
       ).value('.', 'nvarchar(max)') as cleaned
from @data;