Andrey Tsvetkov

const query = `
SELECT 
    A.class, A.fio, A.age, B.teacher_name
FROM 
    students A 
	LEFT JOIN teachers B ON A.class = B.class`

func scan(db *sql.DB) (*MyClass, error) {
	rows, err := db.Query(query)
	if err != nil {
		return nil, err
	}
	class := MyClass{}
	for rows.Next() {
		var a, b, c, d string
		if err := rows.Scan(&a, &b, &c, &d); err != nil {
			return nil, err
		}
		class.Class = a
		class.TeacherName = d
		class.Students = append(class.Students, Student{Age: c, Fio: b})
	}
	return &class, nil
}

if len(settingList) == 0 {
    // данных нет
    return
}
for _, item := range settingList {
    if item.Online == "" {
        item.Online = "не указано"
    }
}

type Task struct {
	Alias string `json:"alias"`
	Data  struct {
		GUID       string `json:"guid"`
		Properties map[string]interface{} `json:"properties"`
		Version string `json:"Version"`
	} `json:"data"`
}