CREATE TABLE writes (paperid NUMBER, authorid NUMBER)
CREATE TABLE keyphrase (keyphraseid NUMBER, keyphrasename VARCHAR2)
CREATE TABLE journal (journalid NUMBER, journalname VARCHAR2)
CREATE TABLE venue (venueid NUMBER, venuename VARCHAR2)
CREATE TABLE dataset (datasetid NUMBER, datasetname VARCHAR2)
CREATE TABLE paperkeyphrase (paperid NUMBER, keyphraseid NUMBER)
CREATE TABLE paperfield (fieldid NUMBER, paperid NUMBER)
CREATE TABLE paperdataset (paperid NUMBER, datasetid NUMBER)
CREATE TABLE cite (citingpaperid NUMBER, citedpaperid NUMBER)
CREATE TABLE author (authorid NUMBER, authorname VARCHAR2)
CREATE TABLE field (fieldid NUMBER)
CREATE TABLE paper (paperid NUMBER, title VARCHAR2, venueid NUMBER, year NUMBER, numciting NUMBER, numcitedby NUMBER, journalid NUMBER)

How many papers did X Jiang co-authored with Frantzen
SELECT DISTINCT COUNT(1) FROM author AS AUTHOR_0, author AS AUTHOR_1, writes AS WRITES_0, writes AS WRITES_1 WHERE AUTHOR_0.authorname = 'X Jiang' AND AUTHOR_1.authorname = 'Frantzen' AND WRITES_0.authorid = AUTHOR_0.authorid AND WRITES_1.authorid = AUTHOR_1.authorid AND WRITES_1.paperid = WRITES_0.paperid
SELECT DISTINCT COUNT(1) FROM "author" "AUTHOR_0" JOIN "writes" "WRITES_0" ON "AUTHOR_0"."authorid" = "WRITES_0"."authorid" JOIN "writes" "WRITES_1" ON "WRITES_0"."paperid" = "WRITES_1"."paperid" JOIN "author" "AUTHOR_1" ON "AUTHOR_1"."authorid" = "WRITES_1"."authorid" AND "AUTHOR_1"."authorname" = 'Frantzen' WHERE "AUTHOR_0"."authorname" = 'X Jiang'