Database: scholar_total_3
Question: main topics of work by Brian DeRenzi
SQL: select distinct t1.keyphrasename , sum ( t1.numcitedby ) from paperkeyphrase_keyphrase_paper_writes_author as t1 where t1.authorname = 'brian derenzi' group by t1.keyphrasename order by sum ( t1.numcitedby ) desc ;