兩張表關聯查詢,學生表和學生學習記錄表,學生表是學生的基本資訊,學習記錄主要是每天背誦的單詞記錄,包括單詞對錯

的個數

ifnull:如果是空則為...

left join左連線,左表全部顯示,右表沒有匹配欄位顯示空

left join後面一張表的查詢結果,用到哪個欄位查詢哪個欄位,沒必要全部查詢

//班級裡的學生單詞背誦查詢

public List<RecitingStudent> findTotalStudents(int classId, Timestamp start, Timestamp end) {
    Session session = getSessionFactory().getCurrentSession();
 
String query = "SELECT s.studentId, s.name, ifnull(sum(m.correct_number),0) as correct, ifnull(sum(m.error_number),0) as error from " +
            "student s " +
            "LEFT JOIN " +
            "(SELECT studentId,correct_number,error_number FROM " +
            "reciting_notes r " +
            "WHERE r.uploadTime BETWEEN ? AND ?) m " 
 
+
            "ON " +
            "s.studentId = m.studentId " +
            "where " +
            "s.classId=? " +
            "GROUP BY s.studentId";
Query query1 = session.createSQLQuery(query).addScalar("studentId",StandardBasicTypes.INTEGER).
            addScalar("name",StandardBasicTypes.STRING
 
).
            addScalar("correct", StandardBasicTypes.INTEGER).
            addScalar("error",StandardBasicTypes.INTEGER);
query1.setParameter(0, start);
query1.setParameter(1, end);
query1.setParameter(2, classId);
List list = query1.list();
List<RecitingStudent> recitingStudents = new ArrayList<>();
    for(Iterator iterator = list.iterator(); iterator.hasNext();){
        //每個集合元素都是一個數組，陣列元素列值
Object[] objects = (Object[]) iterator.next();
RecitingStudent recitingStudent = new RecitingStudent();
recitingStudent.setStudentId((Integer) objects[0]);
recitingStudent.setName((String) objects[1]);
recitingStudent.setCorrect((Integer) objects[2]);
recitingStudent.setError((Integer) objects[3]);
recitingStudents.add(recitingStudent);
}
    return recitingStudents;
}