java - 在JSP中通过PreparedStatement获取数据

Question

当尝试在数据库结果中获取数据时，它为零行，但是当尝试在 mysql 上复制并过去查询时，返回了所需的特定行数。

<小时/>

连接到mysql服务器

<小时/>

private Connection connection() {
    try {
        Class.forName("com.mysql.jdbc.Driver").newInstance();
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/olesdb", "root", "");
    } catch (Exception e) {
        //System.out.println("Connection error");
    }
    return con;
}

**

我的获取数据的函数

**

public List<AcademicYearCourses> getStudentCourse(int studentID, int academicYear,int semester) throws SQLException{
    List<AcademicYearCourses> list = new ArrayList<>();
    PreparedStatement sta = connection().prepareStatement("SELECT courseCode,courseName FROM courses co,studentprograms stpro,academicyearcourse acco WHERE stpro.studentID=? AND acco.academicYearID=? AND acco.semesterID=? AND stpro.programID= acco.programID AND stpro.studyYear=acco.studyYear AND acco.courseID=co.courseID");
    sta.setInt(1, studentID);
    sta.setInt(2, academicYear);
    sta.setInt(3, semester);
    ResultSet res = sta.executeQuery();
    while(res.next()){
        AcademicYearCourses acco = new AcademicYearCourses();
        acco.setAcdemicYearCourseID(rs.getInt("acdemicYearCourseID"));
        acco.setCourseName(rs.getString("courseName"));
        acco.setCourseCode(rs.getString("courseCode"));
        list.add(acco);
    }
    return list;
}

所以我需要帮助来解决这个问题，它在我的项目中非常重要，没有这些数据就无法继续

Answer 1

您正在执行 rs.getInt("acdemicYearCourseID")，但 acdemicYearCourseID 列不在您的 SELECT 列列表中。

另外尝试将 getInt("...")、getString("...") 更改为 getInt(1), getString(2)