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

Where does Peter Mertens publish ?
SELECT DISTINCT paper.journalid, venue.venueid FROM author, paper, venue, writes WHERE author.authorname = 'Peter Mertens' AND venue.venueid = paper.venueid AND writes.authorid = author.authorid AND writes.paperid = paper.paperid
SELECT DISTINCT "paper"."journalid", "venue"."venueid" FROM "author" JOIN "writes" ON "author"."authorid" = "writes"."authorid" JOIN "paper" ON "paper"."paperid" = "writes"."paperid" JOIN "venue" ON "paper"."venueid" = "venue"."venueid" WHERE "author"."authorname" = 'Peter Mertens'