Listing instances that use a security group

Hi all, Is there a cli command to list all the VM's that have a specific security group attached, I need to delete some groups as a tidy up but I only get a warning that it's in use by an instance (of which there's 200) so I'd rather not go through them 1 by 1 in Horizon or show each one on the cli separately. An sql query would be acceptable also but nova db, select * from security_groups; select * from instances; & select * from security_group_instance_association; doesn't give me the required results that I can refine to search deeper. Thanks in advance for any info. Regards,Derek