要求：

頁面：

數據庫設定

主程序

using System;
using System.Data.SqlClient;
using System.Windows.Forms;

namespace Test01
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void BtOK_Click(object sender, EventArgs e)
        {
            SqlConnection conn 
 
= new SqlConnection("server=PC201609230944\\SQL2005;database=HeiMaBlog;user=sa;pwd=123456");
            SqlCommand cmd = new SqlCommand("select *,datediff(minute,LastErrTime,GETDATE()) from UserInfo where UserName=@UserName", conn);
            cmd.Parameters.Add(new SqlParameter("@UserName", TxName.Text.Trim()));
            conn.Open();
            SqlDataReader dr 
 
= cmd.ExecuteReader();

            if (dr.HasRows)
            {
                dr.Read();////不管dr取到多少條數據，只取出前面第一行(調用一次read，就會讀取一行，也只讀取一行)
                if (dr.GetInt32(5) < 15)
                {
                    MessageBox.Show("時間未到，請稍後重試！！");
                    return;
                }

                
 
if (dr[2].ToString() == TxPwd.Text.Trim())
                {
                    MessageBox.Show("登錄成功！！");
                    UserInfo.ReSetErrTimes(dr.GetInt32(0));//登錄成功後，就重置錯誤時間
                }
                else
                {
                    //如果密碼不正確！！
                    MessageBox.Show("登錄失敗，密碼錯誤");
                    UserInfo.UpDateErrTimes(dr.GetInt32(0));
                    // 錯誤三次就更新錯誤時間
                    if (dr.GetInt32(3) + 1 == 3)
                    {
                        UserInfo.UpDateLastErrTime(dr.GetInt32(0));
                        UserInfo.ReSetErrTimes(dr.GetInt32(0));
                    }
                }
            }
            else
            {
                MessageBox.Show("該用戶不存在！！！");
            }
        }
    }
}

輔助

using System.Data.SqlClient;

namespace Test01
{
    class UserInfo
    {
        /// <summary>
        /// 更新錯誤時間！！
        /// </summary>
        /// <param name="id"></param>
        /// <returns></returns>
        public static int UpDateErrTimes(int id)
        {
            using (SqlConnection conn = new SqlConnection("server=PC201609230944\\SQL2005;database=HeiMaBlog;user=sa;pwd=123456"))
            {
                using (SqlCommand cmd = new SqlCommand("update UserInfo set ErrTimes=ErrTimes+1 where id=" + id, conn))
                {
                    conn.Open();
                    return cmd.ExecuteNonQuery();
                }
            }
        }

        /// <summary>
        /// 重置錯誤時間
        /// </summary>
        /// <param name="id"></param>
        /// <returns></returns>
        public static int ReSetErrTimes(int id)
        {
            using (SqlConnection conn = new SqlConnection("server=PC201609230944\\SQL2005;database=HeiMaBlog;user=sa;pwd=123456"))
            {
                using (SqlCommand cmd = new SqlCommand("update UserInfo set ErrTimes=0 where id=" + id, conn))
                {
                    conn.Open();
                    return cmd.ExecuteNonQuery();
                }
            }
        }

        /// <summary>
        /// 更新3次錯誤的輸入時間
        /// </summary>
        /// <param name="id"></param>
        /// <returns></returns>
        public static int UpDateLastErrTime(int id)
        {
            using (SqlConnection conn = new SqlConnection("server=PC201609230944\\SQL2005;database=HeiMaBlog;user=sa;pwd=123456"))
            {
                using (SqlCommand cmd = new SqlCommand("update UserInfo set LastErrTime = getDate() where id= " + id, conn))
                {
                    conn.Open();
                    return cmd.ExecuteNonQuery();
                }

            }

        }

    }
}

Net學習日記_ADO.Net_2_練習（登錄邏輯）