How to add multiple contacts to a group in Google Contacts

Current generally-known practice:

1. Add contact into my/all contacts, if it has never been in yet -- one by one.
2. Select contact(s) from my/all contacts or existing groups, and add to desired group.

Solution: use "Import" function

1. Create CSV file (see: "Creating or editing CSV files").  Just single-column list with header (first line) "Email address" also works. 
2. From GMail or Google-apps, go to Contacts.
3. Click function (at right-end of action bar).
4. Input the CSV file.
5. Enable "Also add these imported contacts to:" and choose (or create new) desired group.
6. Done.  The process will also merged contacts with ones already in Google address book properly.