CREATE TABLE field (fieldid NUMBER)
CREATE TABLE author (authorid NUMBER, authorname VARCHAR2)
CREATE TABLE venue (venueid NUMBER, venuename VARCHAR2)
CREATE TABLE dataset (datasetid NUMBER, datasetname VARCHAR2)
CREATE TABLE paperkeyphrase (paperid NUMBER, keyphraseid NUMBER)
CREATE TABLE paperdataset (paperid NUMBER, datasetid NUMBER)
CREATE TABLE cite (citingpaperid NUMBER, citedpaperid NUMBER)
CREATE TABLE keyphrase (keyphraseid NUMBER, keyphrasename VARCHAR2)
CREATE TABLE paperfield (fieldid NUMBER, paperid NUMBER)
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 writes (paperid NUMBER, authorid NUMBER)

keyphrases used by Akihito Kotera and Masatsugu Kidode
SELECT DISTINCT paperkeyphrase.keyphraseid FROM author, paperkeyphrase, writes WHERE author.authorname IN ('Akihito Kotera', 'Masatsugu Kidode') AND writes.authorid = author.authorid AND writes.paperid = paperkeyphrase.paperid GROUP BY paperkeyphrase.keyphraseid HAVING COUNT(DISTINCT writes.authorid) = 2
SELECT DISTINCT "paperkeyphrase"."keyphraseid" FROM "author" JOIN "writes" ON "author"."authorid" = "writes"."authorid" JOIN "paperkeyphrase" ON "paperkeyphrase"."paperid" = "writes"."paperid" WHERE "author"."authorname" IN ('Akihito Kotera', 'Masatsugu Kidode') GROUP BY "paperkeyphrase"."keyphraseid" HAVING COUNT(DISTINCT "writes"."authorid") = 2