Database: academic
Question: return me the number of authors who have papers in PVLDB .
SQL:
SELECT COUNT ( DISTINCT t1.name ) FROM publication AS t4 JOIN journal AS t2 ON t4.jid  =  t2.jid JOIN writes AS t3 ON t3.pid  =  t4.pid JOIN author AS t1 ON t3.aid  =  t1.aid WHERE t2.name  =  "PVLDB";