java.sql.SQLException : Before start of result set

Question

这里我附上了我的代码，它显示了如下错误: java.sql.SQLException:

在结果集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 结果集循环内为 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，最好使用 JDBC 资源来遍历结果集 1，收集返回的所有“城市”值，然后循环调用 query2 的“城市”结果来获取“州”与“城市”相关联，而不是您所展示的方式。