SQL server extracts pure numbers from strings

One 、 How to extract pure numbers from strings
SQL The statement is as follows （ Example ）：

select a,substring(a,patindex('%[0-9]%', a),
patindex('%[0-9][^0-9]%', a)-patindex('%[0-9]%', a)+1)as only_number
from A

Two 、 design sketch