How many high risk violations do the restaurants in San Francisco have in total?
restaurants in San Francisco refer to business_id where city in ('San Francisco', 'SF', 'S.F.', 'SAN FRANCISCO'); high risk violations refer to risk_category = 'High Risk';
SELECT COUNT(T2.business_id) FROM violations AS T1 INNER JOIN businesses AS T2 ON T1.business_id = T2.business_id WHERE T2.city IN ('San Francisco', 'SF', 'S.F.', 'SAN FRANCISCO') AND T1.risk_category = 'High Risk'