工资系统- '打卡'功能

我正在设计一个使用access数据库作为后端的工资系统。

目前，我正面临实现'clock out'功能的问题。

'clock in'按钮将时间插入数据库。但是，当单击"clock out"按钮时，它将数据插入到新行中。是否有任何方法可以避免这种情况，并根据雇员名称更新现有的最后一行。我尝试过用不同的方法来解决这个问题，但到目前为止，我还没能解决它。

有什么方法可以纠正这个问题吗?

我想我必须在某个地方实现一个循环来检查emp名称，时钟输入并在时钟输出字段中找到空值。我不确定。

请建议。我的代码如下:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public partial class timecards : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        {
            if (Session["ID"] != null && Session["ID"].ToString() != "")
            {
                PanelUsersInfo.Visible = true;
            }
            else
            {
                PanelUsersInfo.Visible = false;
            }
            empLabel.Visible = false;
            mainPagebutton.Visible = false;
            logoutButton.Visible = false;
            if (Session["Title"] == null || Session["Names"] == null)
            {
                clockPanel.Visible = false;
                return;
            }
            else
            {
                mainPagebutton.Visible = true;
                logoutButton.Visible = true;
                empLabel.Visible = true;
                empLabel.Text = "<b>Hi, " + Session["Names"].ToString() + "</b>";
                nameLabel.Text = Session["Names"].ToString();
                clockinLabel.Text = DateTime.Now.ToString("HH:mm");
                Label1.Text = clockinLabel.Text;
            }
        }
    }


    protected void mainPage_Click(object sender, EventArgs e)
    {
        Response.Redirect("employeeLoggedin.aspx");
    }
    protected void logout_Click(object sender, EventArgs e)
    {
        Session.Abandon();
        Response.Redirect("default.aspx");
    }
    protected void clockinButton_Click(object sender, EventArgs e)
    {
        informLabel.Text = "Clocked in at " + Label1.Text + "";
        Label1.Visible = false;
        Label2.Visible = false;
        clockinButton.Enabled = false;
        clockoutButton.Enabled = true;
        string connectionString = "provider=Microsoft.Jet.OLEDB.4.0;" + "data source=" + Page.Server.MapPath("App_Data''database.mdb");
        System.Data.OleDb.OleDbConnection conn = new System.Data.OleDb.OleDbConnection(connectionString);
        System.Data.OleDb.OleDbCommand cmd = conn.CreateCommand();

        cmd.Parameters.Add("Employee", System.Data.OleDb.OleDbType.VarChar);
        cmd.Parameters["Employee"].Value = nameLabel.Text;
        cmd.Parameters.Add("Clockin", System.Data.OleDb.OleDbType.VarChar);
        cmd.Parameters["Clockin"].Value = clockinLabel.Text;
        cmd.CommandText = "INSERT INTO [timecard] ([Employee], [Clockin]) VALUES (@Employee, @Clockin)";
        conn.Open();
        cmd.ExecuteNonQuery();
        conn.Close();


    }
    protected void clockoutButton_Click(object sender, EventArgs e)
    {
        clockoutLabel.Visible = true;
        clockoutLabel.Text = "You have now been clocked out.";
        informLabel.Visible = false;
        Label1.Visible = false;
        clockoutButton.Enabled = false;
        infoLabel.Visible = true;
        infoLabel.Text = "If you want to clock in again, please select timecard option from the main employee page.";

        string connectionString = "provider=Microsoft.Jet.OLEDB.4.0;" + "data source=" + Page.Server.MapPath("App_Data''database.mdb");
        System.Data.OleDb.OleDbConnection conn = new System.Data.OleDb.OleDbConnection(connectionString);
        System.Data.OleDb.OleDbCommand cmd = conn.CreateCommand();
        cmd.Parameters.Add("Employee", System.Data.OleDb.OleDbType.VarChar);
        cmd.Parameters["Employee"].Value = this.nameLabel.Text;
        //String x = DateTime.Now.ToString("HH:mm");
        cmd.Parameters.Add("Clockout", System.Data.OleDb.OleDbType.VarChar);
        cmd.Parameters["Clockout"].Value = this.clockinLabel.Text;

        cmd.CommandText = "UPDATE [timecard] SET [Employee]=@Employee, [Clockout]=@Clockout";


            conn.Open();
            int numberOfRows = cmd.ExecuteNonQuery();
            conn.Close();

    }
}