我正在制作INSERT一个 sql 数据库。并且发生了一件奇怪的事情：当我运行 downer 代码时，数据库被正确写入，但编译器给了我一个错误
java.sql.SQLException: Illegal operation on empty result set.
我还没有搜索过它，我发现它可能是由于 JDBC 驱动程序的错误（但我不这么认为）。所以我决定在这里发帖。
首先我给你数据库表：
表主题
+------------------+----------------+------------+
| subjectCode | SubjectName | teacherCode|
+------------------+----------------+------------+
| 1 | Maths | 10 |
| 2 | English | 20 |
| 3 | Greek | 30 |
+------------------+----------------+------------+
表类
+------------------+----------------+
| ClassCode | ClassName |
+------------------+----------------+
| 1 | Class1 |
| 2 | Class2 |
| 3 | Class3 |
+------------------+----------------+
表课程（row 和 col 是时间表的行（小时）和列（天），它们明确地确定时间表中的课程；例如：小时 1 是一天的第一个小时）
+------------------+----------------+------------+-----------+-------+-------+
| LessonCode | SubjectCode | teacherCode| ClassCode | Day | Hour |
+------------------+----------------+------------+-----------+-------+-------+
| 1 | James | 10 | 1 | 1 | 1 |
| 2 | John | 20 | 2 | 1 | 2 |
| 3 | Frank | 30 | 3 | 1 | 3 |
+------------------+----------------+------------+-----------+-------+-------+
代码：
private void writeLesson(String subjectName, String className, int column, int row)
{
try{
int subjCode;
String query="SELECT subjectCode from subject WHERE subjectName='"+subjectName+"';";
rs = st.executeQuery(query);
rs.next();
subjCode = rs.getInt("subjectCode");
int teacherCode;
String query1="SELECT teacherCode from subject WHERE subjectName='"+subjectName+"';";
rs = st.executeQuery(query1);
rs.next();
teacherCode = rs.getInt("teacherCode");
int classCode;
String query2="SELECT classCode from class WHERE className='"+className+"';";
rs = st.executeQuery(query2);
rs.next();
ClassCode = rs.getInt("classCode");
String query3 ="INSERT INTO lesson (subjCode, classCode, teacherCode, day, hour) "
+ "VALUES ('" + subjCode + "',"
+ "'" + classCode + "',"
+ "'" + teacherCode + "',"
+ "'" + column + "',"
+ "'" + row + "');";
PreparedStatement statement=con.prepareStatement(query3);
statement.executeUpdate();
statement.close();
}
catch (Exception ex){
System.out.println("Error db: "+ex);
重要提示：该方法writeLesson位于cycle. 我没有在一个循环中测试过这段代码，它可以工作。为什么在你看来？
解决方案：问题是在循环中，writeLesson我传递给它的方法是“空白”字符串，导致错误（这就是在 DB 上写入工作的原因，但出现错误）。