CREATE TABLE acceptance (submission_id NUMBER, workshop_id NUMBER, result CLOB)
CREATE TABLE workshop (workshop_id NUMBER, date CLOB, venue CLOB, name CLOB)
CREATE TABLE submission (submission_id NUMBER, scores NUMBER, author CLOB, college CLOB)

Which authors did not submit to any workshop?
SELECT author FROM submission WHERE NOT submission_id IN (SELECT submission_id FROM acceptance)
SELECT "author" FROM "submission" WHERE NOT "submission_id" IN (SELECT "submission_id" FROM "acceptance")