Listing 1: Code Example for Retrieving Only Numeric Part of String
DECLARE @str nvarchar(255)
SET @str = N'qq23.34' -- 23
--SET @str = null -- null
--SET @str = N'' – empty string
--SET @str = N'%' – empty string
--SET @str = N'2' -- 2
--SET @str = N'abc' – empty string
--SET @str = N'a23b' -- 23

/* Add a non-numeric string terminator. */
SELECT @str = @str + N'X'

/* Remove all non-numerics from the head of the string by finding the first numeric. */
SELECT @str = right(@str,len(@str) - PATINDEX(N'%[0-9]%',@str) + 1)

/* Remove all non-numerics from the tail of the string by finding the first non-numeric. */
SELECT @str = left(@str, PATINDEX(N'%[^0-9]%',@str) - 1)

SELECT @str