student_grades数据表中重要字段有total_score（最终成绩），id（用户id）,class_id（班级id）

要求一个sql查询出某个班的学生总数，有成绩的数量，无成绩的数量，60以下，60-79，80以上的数量，最高分，最低分，平均分

SELECT
		COUNT(id) AS totalUser,
		COUNT(total_score IS NOT NULL OR NULL) AS hasScore,
		COUNT(total_score IS NULL OR NULL) AS noScore,
		COUNT(total_score >= 80 OR NULL) AS higherThan80,
		COUNT(total_score >= 60 AND total_score < 80 OR NULL) AS between60to79,
		COUNT(total_score < 60 OR NULL) AS lessThan60,
		IFNULL(MAX(total_score),0) AS maxScore,
		IFNULL(MIN(total_score),0) AS minScore,
		IFNULL(CAST(AVG(total_score) AS DECIMAL(10,2)),0) AS avgScore
FROM
    statistic_student_grades
WHERE class_id = #{classId,jdbcType=INTEGER}

tips:
count()函数只有在值为null时才不统计数据，而为false时是会统计数据的，因此需要加上or null，既当条件不满足时不进行统计