CREATE TABLE author (authorid NUMBER, authorname VARCHAR2)
CREATE TABLE venue (venueid NUMBER, venuename VARCHAR2)
CREATE TABLE paperfield (fieldid NUMBER, paperid NUMBER)
CREATE TABLE writes (paperid NUMBER, authorid NUMBER)
CREATE TABLE paperdataset (paperid NUMBER, datasetid NUMBER)
CREATE TABLE paperkeyphrase (paperid NUMBER, keyphraseid NUMBER)
CREATE TABLE cite (citingpaperid NUMBER, citedpaperid NUMBER)
CREATE TABLE dataset (datasetid NUMBER, datasetname VARCHAR2)
CREATE TABLE keyphrase (keyphraseid NUMBER, keyphrasename VARCHAR2)
CREATE TABLE journal (journalid NUMBER, journalname VARCHAR2)
CREATE TABLE paper (paperid NUMBER, title VARCHAR2, venueid NUMBER, year NUMBER, numciting NUMBER, numcitedby NUMBER, journalid NUMBER)
CREATE TABLE field (fieldid NUMBER)

Since 2011 who has published works about IBD ( Inflammatory Bowel Disease ) and diet ?
SELECT DISTINCT writes.authorid FROM keyphrase, paper, paperkeyphrase, writes WHERE keyphrase.keyphrasename IN ('IBD', 'diet') AND paperkeyphrase.keyphraseid = keyphrase.keyphraseid AND paper.paperid = paperkeyphrase.paperid AND paper.year > 2011 AND writes.paperid = paper.paperid GROUP BY writes.authorid
SELECT DISTINCT "writes"."authorid" FROM "keyphrase" JOIN "paperkeyphrase" ON "keyphrase"."keyphraseid" = "paperkeyphrase"."keyphraseid" JOIN "paper" ON "paper"."paperid" = "paperkeyphrase"."paperid" AND "paper"."year" > 2011 JOIN "writes" ON "paper"."paperid" = "writes"."paperid" WHERE "keyphrase"."keyphrasename" IN ('IBD', 'diet') GROUP BY "writes"."authorid"