Pad single digit numbers in column with leading zero

I have a requirement to pad any single digit numbers in a string field with a leading zero. I only need to pad single numeric characters with a leading zero, not string alphabetic characters (A-Z). Below is an example of the current data, along with the expected output for these examples.

Current output     Expected output:
9                  09    
19                 19   
15                 15
F                  F
UR                 UR           
B                  B  
0                  00    
4                  04
N                  N
00                 00

>Solution :

Use a CASE expression to check whether the column contains only 0 to 9. If true then prefix with 0 else as it is.

Query

select 
  case when col like '[0-9]' 
    then '0' + col
  else col end as newcol  
from tablename;