Database: scholar_minus_1_4
Question: How many papers did David M. Blei publish at AISTATS ?
SQL: select distinct count ( t1.paperid ) from venue_paper as t1 join writes as t2 on t1.paperid = t2.paperid join author as t3 on t2.authorid = t3.authorid where t3.authorname = 'david m. blei' and t1.venuename = 'aistats' ;