JDBC从访问表中选择最大值 [英] JDBC selecting the Max value from an Access table

问题描述

即使我的表中存在该列，只要运行以下代码，我都会收到错误消息找不到列".我正在使用访问数据库，请寻求帮助

I got error "Column not found" any time i run the following code even though the column exist in my table. Am using access database, Appealing for help please

public class Trial1 {
public static void main (String[]args){

            try{
                Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");  
                String url = "jdbc:odbc:SENSOR";
                String user = "";
                String pass = "";
                Connection con = DriverManager.getConnection(url,user,pass);
                Statement stmt  = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);                          //stmt代表資料庫連接成功


                ResultSet rs = stmt.executeQuery("select MAX(LevelNum) from NList");
                 if (rs.next()){

                    int w = rs.getInt("LevelNum");
                   int x= 3;                             

                double i = Math.pow(2, (w-x))-1;
                System.out.printf("i is  %f",i);}


                stmt.close();
                con.close();

            }catch(Exception e)
            {
                System.out.println("Error" + e);
            }

}

}

推荐答案

假设错误是在获取结果时而不是在执行查询时发生的，则可能需要这样的东西

Assuming the error is when you get the result rather than when you execute the query, you probably need something like this instead

// ...
ResultSet rs = stmt.executeQuery("select MAX(LevelNum) as maxLevel from NList");
if (rs.next())
{
    int w = rs.getInt("maxLevel");

    // ... etc.
}

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