Well, but you can specify a new empty log file. In the past we did it with sp_attach_single_file_db, in this case a new log file is generated. Now you have to use CREATE DATABASE database_name FOR ATTACH instead as indicated in the article for sp_attach_single_file_db

CREATE DATABASE database_name FOR ATTACH has an option to rebuild the log. The ATTACH_REBUILD_LOG automatically creates a new, 1-MB log file as CREATE DATABASE article says.

I used detaching and attaching a database to replace an old big log with a new empty one.

Yelena