如何检查数据库是否有测验，并向系统管理员显示消息

你不需要为阅读器使用While，因为你只需要一个quizid，你可以在发送邮件之前使用if子句来检查是否有quizid

protected void SendEmail(string toAddresses, string fromAddress, string MailSubject, string MessageBody, bool isBodyHtml)
    {
        SmtpClient sc = new SmtpClient("MAIL.Aramco.com");
        try
        {
            MailMessage msg = new MailMessage();
            msg.From = new MailAddress("pssp@aramco.com", "PMOD Safety Services Portal (PSSP)");
            // In case the mail system doesn't like no to recipients. This could be removed
            //msg.To.Add("pssp@aramco.com");
            msg.Bcc.Add(toAddresses);
            msg.Subject = MailSubject;
            msg.Body = MessageBody;
            msg.IsBodyHtml = isBodyHtml;
            //Response.Write(msg);
            sc.Send(msg);
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }
    protected void SendEmailTOAllUser()
    {
        string connString = "Data Source=localhost''sqlexpress;Initial Catalog=psspdbTest;Integrated Security=True";
        using (SqlConnection conn = new SqlConnection(connString))
        {
            var sbEmailAddresses = new System.Text.StringBuilder(2000);
            string quizid = "";
            // Open DB connection.
            conn.Open();
            string cmdText = "SELECT MIN (QuizID) As mQuizID FROM dbo.QUIZ WHERE IsSent <> 1";
            using (SqlCommand cmd = new SqlCommand(cmdText, conn))
            {
                SqlDataReader reader = cmd.ExecuteReader();
                if (reader != null)
                {
                    if(reader.Read())
                    {
                        // There is only 1 column, so just retrieve it using the ordinal position
                        quizid = reader["mQuizID"].ToString();
                    }
                }
                reader.Close();
            }
            string cmdText2 = "SELECT Username FROM dbo.employee";
            using (SqlCommand cmd = new SqlCommand(cmdText2, conn))
            {
                SqlDataReader reader = cmd.ExecuteReader();
                if (reader != null)
                {
                    while (reader.Read())
                    {
                        var sName = reader.GetString(0);
                        if (!string.IsNullOrEmpty(sName))
                        {
                            if (sbEmailAddresses.Length != 0)
                            {
                                sbEmailAddresses.Append(",");
                            }
                            // Just use the ordinal position for the user name since there is only 1 column
                            sbEmailAddresses.Append(sName).Append("@aramco.com");
                        }
                    }
                }
                reader.Close();
            }
            string cmdText3 = "UPDATE dbo.Quiz SET IsSent = 1 WHERE QuizId = @QuizID";
            using (SqlCommand cmd = new SqlCommand(cmdText3, conn))
            {
                // Add the parameter to the command
                var oParameter = cmd.Parameters.Add("@QuizID", SqlDbType.Int);
                var sEMailAddresses = sbEmailAddresses.ToString();
                string link = "<a href='http://pmv/pssp/StartQuiz.aspx?testid=" + quizid + "'> Click here to participate </a>";
                string body = @"Good day, <br /><br />
                                <b> Please participate in the new short safety quiz </b>"
                                    + link +
                                    @"<br /><br />
                            Also, give yourself a chance to gain more safety culture by reading the PMOD Newsletter.
                            <br /> <br /><br /> <br />
                            This email was generated using the <a href='http://pmv/pssp/Default.aspx'>PMOD Safety Services Portal (PSSP) </a>. 
                            Please do not reply to this email.
                            ";
                int sendCount = 0;
                List<string> addressList = new List<string>(sEMailAddresses.Split(','));
                StringBuilder addressesToSend = new StringBuilder();
if(!string.IsNullOrEmpty(quizid )){
                for (int userIndex = 0; userIndex < addressList.Count; userIndex++)
                {
                    sendCount++;
                    if (addressesToSend.Length > 0)
                        addressesToSend.Append(",");
                    addressesToSend.Append(addressList[userIndex]);
                    if (sendCount == 10 || userIndex == addressList.Count - 1)
                    {
                        SendEmail(addressesToSend.ToString(), "", "Notification of New Weekly Safety Quiz", body, true);
                        addressesToSend.Clear();
                        sendCount = 0;
                    }
                }
}
                // Update the parameter for the current quiz
                oParameter.Value = quizid;
                // And execute the command
                cmd.ExecuteNonQuery();
            }
            conn.Close();
        }
    }

最简单的解决方案是执行标量查询来确定行数：

SELECT COUNT(*) FROM Quiz

如果这大于零，表中还有测验！

您已经得到了quizid。如果为空，请发送电子邮件给管理员并返回，否则在…之前。。。？

在SendEmailTOAllUser中使用选择最小quizid的块后，您应该检查quizid是否为null，并将代码嵌入到conn.Close（）中。