Question

这里我附上了我的代码，它显示的错误如下： java.sql.SQLException：

在结果开始之前，我在这里做错了什么：

String qry = "SELECT * From register ";



stmt = (PreparedStatement) conn.prepareStatement(qry);
rs =  stmt.executeQuery();
while (rs.next()) {
    String area = rs.getString("city");
    if(city.equals(area)){
        System.out.println("!!!!!!It matched: " + city);
        String qry2="select state from register where city='"+city+"'";
        System.out.println(qry2);
        stmt = (PreparedStatement) conn.prepareStatement(qry2);
        rs =  stmt.executeQuery();
        String state=rs.getString("state");
        System.out.println("state: " + state);
        break;
    } else {
        //System.out.println("No match with: " + area);
    }
}

Answer 1

您可以在query1结果集循环中为query2使用新的ResultSet对象。

String qry2="select state from register where city='"+city+"'";
System.out.println(qry2);
stmt = (PreparedStatement) conn.prepareStatement(qry2);
ResultSet rs2 =  stmt.executeQuery();
String state=rs2.getString("state");

但一般来说，更好地利用JDBC资源来遍历结果集1，收集返回的所有“city”值，然后遍历“city”结果调用query2来获取“状态”与“城市”相关联，而不是你们表现出来的方式。

Answer 2

您的代码中不需要第二个结果集。 State 和 City 都可以在同一个结果集中找到。您可以使用以下代码：

String qry = "select * from register";
PreparedStatement stmt = (PreparedStatement) conn.prepareStatement(qry);
             rs =  stmt.executeQuery();
             while (rs.next()) {
                 String area = rs.getString("city");
                 if(city.equals(area)){
                    System.out.println("!!!!!!It matched: " + city);
                    String state=rs.getString("state");
                    System.out.println("state: " + state);
                    break;
                 } else {
                    //System.out.println("No match with: " + area);
                 }
           }

java.sql.SQLException：在结果集开始之前

2 个答案: