using System;

using System.Collections.Generic;

using System.Text;

using System.Data;

using System.Data.OleDb;

//数据类

namespace winfamily

{

    class DBconn

    {

      private OleDbConnection conn;

        //属性

        public OleDbConnection Conn

        {

            get { return conn; }

        }

        //连接数据库

        public  DBconn(string sql)

        {

            conn = new OleDbConnection(sql);

        }

        //取得数据集

        public DataSet getdb(string str)

        {  

            Conn.Open();

            OleDbDataAdapter oleda;

            oleda = new OleDbDataAdapter(str,Conn);

            DataSet ds = new DataSet();

            oleda.Fill(ds);

            //关闭

            Conn.Close();

            return ds;

        }

    }

}

<?xml version="1.0" encoding="utf-8" ?>

    <add key="sql" value="provider=Microsoft.Jet.OLEDB.4.0;data source=db.mdb"/>

---------------------------

提交消费信息的代码（当然，最好使用参数插入到数据库）：

//提交消费信息到数据库

    private void button1_Click(object sender, EventArgs e)

    {

        //得到数据库 表需要的数据

        string time = xfDatetime.Text;

        string type = xfType.SelectedItem.ToString();

        double money =double.Parse(xfMoney.Text);

        string address = xfAddress.Text;

        string person = xfPerson.Text;

        string info = xfInfo.Text;

        //插入数据

        string str = "insert into expenditure(消费日期,消费类别,消费金额,消费地点,消费者,备注说明) " +

            "values(#" + time + "#,'" + type + "'," + money + ",'" + address + "','" + person + "','" + info + "')";

        //执行SQL操作

        DBconn dbClass = new DBconn(sql);

        OleDbCommand command = new OleDbCommand(str, dbClass.Conn);

        dbClass.Conn.Open();

        command.ExecuteNonQuery();

        dbClass.Conn.Close();

        MessageBox.Show("提交成功！");

    }

//查询信息

    private void button2_Click(object sender, EventArgs e)

    {

        //查询语句

        string str = "select * from expenditure ";

        if (cxType.SelectedItem.ToString().Trim() != "")

            str +=  "where 消费类别='" + cxType.SelectedItem.ToString()+"'";

        if (cxperson.SelectedItem.ToString().Trim() != "")

            str +=  " and  消费者='" + cxperson.SelectedItem.ToString()+"'";

        str += " and  消费日期>= #" + cxBegintime.Value.ToShortDateString() + "#  and 消费日期<= #" + cxEndTime.Value.ToShortDateString() + "# ";

        MessageBox.Show(str);

        //执行查询 

        DBconn dbClass=new DBconn(sql);

        OleDbCommand olecommand = new OleDbCommand(str, dbClass.Conn);

        dbClass.Conn.Open();

        olecommand.ExecuteNonQuery();

        dbClass.Conn.Close();

        //显示查询

        DataSet ds = dbClass.getdb(str);

        dataGridView1.DataSource = ds.Tables[0];

    }

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一小段代码！