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

Which paper first used Decision Feedback for Multiuser Receiver ?
SELECT DISTINCT paper.paperid, paper.year FROM keyphrase, paper, paperkeyphrase WHERE keyphrase.keyphrasename IN ('Multiuser Receiver', 'Decision Feedback') AND paperkeyphrase.keyphraseid = keyphrase.keyphraseid AND paper.paperid = paperkeyphrase.paperid GROUP BY paper.paperid, paper.year HAVING COUNT(DISTINCT keyphrase.keyphrasename) > 1 ORDER BY paper.year
SELECT DISTINCT "paper"."paperid", "paper"."year" FROM "keyphrase" JOIN "paperkeyphrase" ON "keyphrase"."keyphraseid" = "paperkeyphrase"."keyphraseid" JOIN "paper" ON "paper"."paperid" = "paperkeyphrase"."paperid" WHERE "keyphrase"."keyphrasename" IN ('Multiuser Receiver', 'Decision Feedback') GROUP BY "paper"."paperid", "paper"."year" HAVING COUNT(DISTINCT "keyphrase"."keyphrasename") > 1 ORDER BY "paper"."year" NULLS FIRST