In how many papers and in what years was the International Conference on Database Theory published?
the International Conference on Database Theory refers to FullName = 'International Conference on Database Theory'; published refers to year ! = 0
SELECT COUNT(T1.Id) AS PAPER, COUNT(DISTINCT T1.Year) AS YEARS FROM Paper AS T1 INNER JOIN Conference AS T2 ON T1.ConferenceId = T2.Id WHERE year != 0 AND T2.FullName = 'International Conference on Database Theory'