SQL Overelaboration

Random forum posting, function that detects if a string is made only of numbers:

CREATE function fn_numeric
-- input is varchar string.
   (@string varchar(12) )
returns bit -- 0 = false, 1 = true
as
begin
declare @x smallint, @y smallint, @z bit
set @string = replace(@string, ' ', '@')
set @x = len(@string)
set @y = 0
set @z = 1
while @y < @x
    begin
    set @y = @y + 1
    if substring(@string, @y, 1) between '0' and '9'
        continue
    else
        begin
        set @z = 0
        break
        end
    end
return (@z)
end

My response:

WHERE ColumnToTest NOT LIKE '%[^0-9]%'