You may use the Groupfilter in Admin->User Accounts.
Or:
select * from egw_accounts where account_id in (SELECT acl_account FROM
egw_acl where acl_appname=‘phpgw_group’ and acl_location = (select
account_id*-1 from egw_accounts where account_lid=‘YOUR-PRECIOUS-GROUP’ and
account_type=‘g’)) and account_type=‘u’ ;