Question

    private void CoursesOfStudent () throws SQLException, IOException {
    try {
        String sql = "SELECT Students.StudentId, Students.Name, Courses.Name,Grade\n"
                + " FROM Students LEFT JOIN StudentCourses\n"
                + "ON Students.StudentId = StudentCourses.StudentId\n"
                + "LEFT JOIN Courses ON Courses.CourseId = StudentCourses.CourseId\n"
                + "WHERE Students.StudentId = ?";
        pre = connection.prepareStatement(sql);
        System.out.print("Let put Id of student that you wanna list all of courses: ");
        int Stid = Integer.parseInt(reader.readLine());
        pre.setInt(1, Stid);
        ResultSet rs = stmt.executeQuery(sql);
         while (rs.next()) {
            Stid = rs.getInt("StudentId");
            String Stname = rs.getString("Students.Name");
            String Coname = rs.getString("Courses.Name");
            int grade = rs.getInt("Grade");

            System.out.print("StudentId: " + Stid);
            System.out.print(", StudentName: " + Stname);
            System.out.print(", CourseName: " + Coname);
            System.out.println(", Grade: " + grade);
        }
         pre.executeUpdate();
    }catch (SQLException se) {
        se.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

我想加入并在JDBC中的不同表中显示列，但它有一些错误，谁可以帮助我........................ ........................................... 非常感谢！

这是错误：

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '?' at line 5

Answer 1

听起来你的MySQL / MySQL JDBC驱动程序无法处理准备好的语句。

问：您使用的是MySQL 5.0或更高版本吗？

ALSO：

确保所有SQL语句之间都有空格。不要依赖“\ n”：

实施例

String sql = "SELECT Students.StudentId, Students.Name, Courses.Name,Grade\n"
                + " FROM Students LEFT JOIN StudentCourses\n"
                + " ON Students.StudentId = StudentCourses.StudentId\n"
                + " LEFT JOIN Courses ON Courses.CourseId = StudentCourses.CourseId\n"
                + " WHERE Students.StudentId = ?";

Answer 2

我认为你应该尝试使用;之后？同样。休息取决于您使用的驱动程序版本。

Answer 3

您使用了错误的executeQuery方法。当您使用PreparedStatement时，在执行先前准备的语句时，应使用不带字符串参数的executeQuery()。

所以使用：

ResultSet rs = stmt.executeQuery();

如果你使用executeQuery that takes a string，JDBC api甚至需要准备好的语句抛出SQLException：

<强>抛出：
SQLException - ...，该方法在PreparedStatement或CallableStatement
上调用

我如何从jdbc中的不同表连接记录

3 个答案: