In which regions are there no pizza restaurants?
no pizza restaurants refers to food_type = 'pizza'
SELECT DISTINCT T2.region FROM generalinfo AS T1 INNER JOIN geographic AS T2 ON T1.city = T2.city WHERE T1.food_type = 'pizza' AND T2.region != 'unknown'
database name:db_id restaurant
geographic table geographic Cols: city dtype text, country dtype text, region dtype text, 
generalinfo table generalinfo Cols: id restaurant dtype integer, label dtype text, food type dtype text, city dtype text, review dtype real, 
location table location Cols: id restaurant dtype integer, street number dtype integer, street name dtype text, city dtype text, 
