return me the total citations of papers in the VLDB conference in each year .
SELECT t2.year  ,  SUM ( t2.citation_num ) FROM publication AS t2 JOIN conference AS t1 ON t2.cid  =  t1.cid WHERE t1.name  =  "VLDB" GROUP BY t2.year;
SELECT t2.year  ,  SUM ( t2.citation_num ) FROM publication AS t2 JOIN conference AS t1 ON t2.cid  =  t1.cid WHERE t1.name  =  "VLDB" GROUP BY t2.year;
[{'Nenhum': 'Nenhum resultado encontrado'}]