return me the number of papers on PVLDB .
SELECT COUNT ( DISTINCT t2.title ) FROM publication AS t2 JOIN journal AS t1 ON t2.jid  =  t1.jid WHERE t1.name  =  "PVLDB";
SELECT COUNT ( DISTINCT t2.title ) FROM publication AS t2 JOIN journal AS t1 ON t2.jid  =  t1.jid WHERE t1.name  =  "PVLDB";
[{'COUNT ( DISTINCT t2.title )': 0}]