Which accelerators are compatible with at least one browser?
select name from web_client_accelerator where id in (select accelerator_id from accelerator_compatible_browser)
Which are compatible with none?
select name from web_client_accelerator where id not in (select accelerator_id from accelerator_compatible_browser)
What are the ids and names of the web accelerators that are compatible with two or more browsers?
select t1.id, t1.name from web_client_accelerator as t1 join accelerator_compatible_browser as t2 on t2.accelerator_id = t1.id group by t1.id having count(*) >= 2