Database: scholar
Question: When was deep learning proposed ?
SQL:
SELECT DISTINCT t3.year FROM paperkeyphrase AS t2 JOIN keyphrase AS t1 ON t2.keyphraseid  =  t1.keyphraseid JOIN paper AS t3 ON t3.paperid  =  t2.paperid WHERE t1.keyphrasename  =  "deep learning" GROUP BY t3.year ORDER BY t3.year ASC;