Database: food_inspection
Question: What is the average score for "Chairman Bao" in all its unscheduled routine inspections?
SQL: SELECT CAST(SUM(CASE WHEN T2.name = 'Chairman Bao' THEN T1.score ELSE 0 END) AS REAL) / COUNT(CASE WHEN T1.type = 'Routine - Unscheduled' THEN T1.score ELSE 0 END) FROM inspections AS T1 INNER JOIN businesses AS T2 ON T1.business_id = T2.business_id