CREATE TABLE acceptance (Submission_ID VARCHAR, workshop_id VARCHAR)
CREATE TABLE submission (Author VARCHAR, Submission_ID VARCHAR)

Show the authors who have submissions to more than one workshop.
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
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