Subdomain in same zonefile`

[Jon Booth]

Is this possible and if not what is the best way?

$ORIGIN mydomain.com.
hosta	IN	A	123.123.123.123
hostb	IN	A	123.123.123.124
*.hosta	IN	CNAME	hosta.domain.com.

Or do I have to have a separate zone file for *.hosta.domain.com?

Hope this makes sense and any help appreciated.
Jon