retrieving numeric number and special character

select charindex('_',[Fieldname]) will give an integer for the underscore

select substring([Fieldname],start,length) will reduce the string

use a combination to reduce your field as required. You will need nested queries to do this.

Slightly modified from the answer given here[^]
Check if it may help you

DECLARE @InputString NVARCHAR(MAX)
DECLARE @Delimiter NVARCHAR(40)
DECLARE @Pos INT
DECLARE @NextString NVARCHAR(40)
SET @InputString = '20112312438_AjaxURLS.txt_123546675'
SET @Delimiter = 1
SET @Pos = 1
SET @InputString = @InputString + @Delimiter
CREATE TABLE #Results(Tokens NVARCHAR(MAX))
WHILE (@pos<>0)
BEGIN
    SET @NextString = replace(@inputstring,@delimiter,'')
    set @delimiter=@delimiter+1
    INSERT INTO #Results VALUES (@NextString)
    update #results set tokens=@nextstring
    SET @InputString = replace(@NextString,'_','')
    SET @pos = charindex(@Delimiter,@InputString)
END
SELECT distinct replace(tokens,'0','') FROM #Results
DROP TABLE #Results