Select query to remove non-numeric characters

Here is an elegant solution if your server supports the TRANSLATE function (on sql server it's available on sql server 2017+ and also sql azure).

First, it replaces any non numeric characters with a @ character. Then, it removes all @ characters. You may need to add additional characters that you know may be present in the second parameter of the TRANSLATE call.

select REPLACE(TRANSLATE([Col], 'abcdefghijklmnopqrstuvwxyz+()- ,#+', '@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@'), '@', '')

You can use stuff and patindex.

stuff(Col, 1, patindex('%[0-9]%', Col)-1, '')

SQL Fiddle

See this blog post on extracting numbers from strings in SQL Server. Below is a sample using a string in your example:

DECLARE @textval NVARCHAR(30)
SET @textval = 'AB ABCDE # 123'

SELECT LEFT(SUBSTRING(@textval, PATINDEX('%[0-9.-]%', @textval), 8000),
           PATINDEX('%[^0-9.-]%', SUBSTRING(@textval, PATINDEX('%[0-9.-]%', @textval), 8000) + 'X') -1)