CREATE TABLE domain_publication (did NUMBER, pid NUMBER)
CREATE TABLE conference (cid NUMBER, homepage VARCHAR2, name VARCHAR2)
CREATE TABLE domain_journal (did NUMBER, jid NUMBER)
CREATE TABLE domain (did NUMBER, name VARCHAR2)
CREATE TABLE keyword (keyword VARCHAR2, kid NUMBER)
CREATE TABLE domain_keyword (did NUMBER, kid NUMBER)
CREATE TABLE organization (continent VARCHAR2, homepage VARCHAR2, name VARCHAR2, oid NUMBER)
CREATE TABLE domain_conference (cid NUMBER, did NUMBER)
CREATE TABLE journal (homepage VARCHAR2, jid NUMBER, name VARCHAR2)
CREATE TABLE domain_author (aid NUMBER, did NUMBER)
CREATE TABLE writes (aid NUMBER, pid NUMBER)
CREATE TABLE cite (cited NUMBER, citing NUMBER)
CREATE TABLE publication_keyword (kid NUMBER, pid NUMBER)
CREATE TABLE author (aid NUMBER, homepage VARCHAR2, name VARCHAR2, oid NUMBER)
CREATE TABLE publication (abstract VARCHAR2, cid NUMBER, citation_num NUMBER, jid NUMBER, pid NUMBER, reference_num NUMBER, title VARCHAR2, year NUMBER)

return me the number of authors who have papers in PVLDB .
SELECT COUNT(DISTINCT (author.name)) FROM author, journal, publication, writes WHERE journal.name = 'PVLDB' AND publication.jid = journal.jid AND writes.aid = author.aid AND writes.pid = publication.pid
SELECT COUNT(DISTINCT "author"."name") FROM "author" JOIN "journal" ON "journal"."name" = 'PVLDB' JOIN "publication" ON "journal"."jid" = "publication"."jid" JOIN "writes" ON "author"."aid" = "writes"."aid" AND "publication"."pid" = "writes"."pid"