How many establishments have an inspection score of no more than 50?
establishments have the same meaning as businesses; inspection score of no more than 50 refers to score < 50;
SELECT COUNT(DISTINCT business_id) FROM inspections WHERE score < 50
database name:db_id food_inspection
businesses table businesses Cols: business id dtype integer, name dtype text, address dtype text, city dtype text, postal code dtype text, latitude dtype real, longitude dtype real, phone number dtype integer, tax code dtype text, business certificate dtype integer, application date dtype date, owner name dtype text, owner address dtype text, owner city dtype text, owner state dtype text, owner zip dtype text, 
inspections table inspections Cols: business id dtype integer, score dtype integer, date dtype date, type dtype text, 
violations table violations Cols: business id dtype integer, date dtype date, violation type id dtype text, risk category dtype text, description dtype text, 
