Database: academic
Question: return me the number of papers in VLDB conference containing keyword " Information Retrieval " .
SQL:
SELECT COUNT ( DISTINCT t4.title ) FROM publication_keyword AS t3 JOIN keyword AS t1 ON t3.kid  =  t1.kid JOIN publication AS t4 ON t4.pid  =  t3.pid JOIN conference AS t2 ON t4.cid  =  t2.cid WHERE t2.name  =  "VLDB" AND t1.keyword  =  "Information Retrieval";