if else

SELECT 
CASE WHEN score > 90 THEN 
	CASE WHEN score >= 95 THEN 'A+' 
		ELSE 'A' 
	END 
	
	WHEN score > 70 THEN 
	CASE WHEN score >= 80 THEN 'B+' 
		ELSE 'B' 
	END 
	
	WHEN score > 50 THEN 
		CASE WHEN score >= 60 THEN 'C+' 
		ELSE 'C' 
	END 
	
	WHEN score > 30 THEN 'D' 
		ELSE 'F' 
	END 
    AS code_score FROM mine