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

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"