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

who works on Multiuser Receiver for Decision Feedback
SELECT DISTINCT writes.authorid FROM keyphrase, paper, paperkeyphrase, writes WHERE keyphrase.keyphrasename IN ('Multiuser Receiver', 'Decision Feedback') AND paperkeyphrase.keyphraseid = keyphrase.keyphraseid AND paper.paperid = paperkeyphrase.paperid AND writes.paperid = paper.paperid GROUP BY writes.authorid HAVING COUNT(DISTINCT keyphrase.keyphrasename) > 1
SELECT DISTINCT "writes"."authorid" FROM "keyphrase" JOIN "paperkeyphrase" ON "keyphrase"."keyphraseid" = "paperkeyphrase"."keyphraseid" JOIN "paper" ON "paper"."paperid" = "paperkeyphrase"."paperid" JOIN "writes" ON "paper"."paperid" = "writes"."paperid" WHERE "keyphrase"."keyphrasename" IN ('Multiuser Receiver', 'Decision Feedback') GROUP BY "writes"."authorid" HAVING COUNT(DISTINCT "keyphrase"."keyphrasename") > 1