Database: academic
Question: return me the number of papers by " H. V. Jagadish " on VLDB conference .
SQL:
SELECT COUNT ( DISTINCT t4.title ) FROM publication AS t4 JOIN conference AS t2 ON t4.cid  =  t2.cid JOIN writes AS t3 ON t3.pid  =  t4.pid JOIN author AS t1 ON t3.aid  =  t1.aid WHERE t1.name  =  "H. V. Jagadish" AND t2.name  =  "VLDB";