Show the authors who have submissions to more than one workshop.
create table submission (author varchar, submission_id varchar, PRIMARY KEY (author)); create table acceptance (submission_id varchar, workshop_id varchar, PRIMARY KEY (submission_id))
select t2.author from acceptance as t1 join submission as t2 on t1.submission_id = t2.submission_id group by t2.author having count(distinct t1.workshop_id) > 1