Sorry again for this basic questions but i see that many developers have not clear ideas

I need that my subdomain load from this 2 url: http://subdomain.example.com BUT ALSO http://www.subdomain.example.com

For this settings i need 2 record A? OR only the first?

subdomain      A       12.34.56.78
www.subdomain  A       12.34.56.78

NB: i ask this information because i see in my Linode DNS Manager that my primary domain have 2 record A:

(nothing) A       12.34.56.78
www       A       12.34.56.78