如何获取 SQL 代码以在用 C# 编写时发送错误消息

我有代码，每个用户上传一个 excel 电子表格，然后上传后，我让它基于另一个 SQL 表更新 SQL 中的一个列。我想验证 Excel 电子表格中的数据是否与 SQL 表中要从中更新的选项之一匹配。最简单的方法是什么？即，如果返回 NULL 值，我可以添加一个 SQL 语句以在网站上给我一条错误消息，还是我必须用 C# 编写一个复杂的 IF 语句？以下是我到目前为止所拥有的（请参阅 SQL 语句）：

try
    {
        FileUpload.SaveAs(path);
        if (TextBox.Text != "")
        sheetname = TextBox.Text;
        System.Data.OleDb.OleDbConnection MyConnection;
        System.Data.DataSet DtSet;
        System.Data.OleDb.OleDbDataAdapter MyCommand;  //check sheet name
        MyConnection = new System.Data.OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + path + ";Extended Properties=Excel 12.0;");
        MyCommand = new System.Data.OleDb.OleDbDataAdapter("select * from [" + sheetname + "$]", MyConnection);
        //MyCommand = new System.Data.OleDb.OleDbDataAdapter("select * from [July Noms$]", MyConnection);
        MyCommand.TableMappings.Add("Table", "TestTable");
        DtSet = new System.Data.DataSet();
        MyCommand.Fill(DtSet);
        SqlConnection curConnection = new SqlConnection(@"Data Source=1tc-Techcomm2;Initial Catalog=EventRegistration;Integrated Security=True");
        curConnection.Open();
        SqlCommand curCommand;
        SqlParameter param;
        string str;
        for (int i = 0; i < DtSet.Tables[0].Rows.Count; i++)
        {
            if (DtSet.Tables[0].Rows[i][1] == DBNull.Value)
                continue;
            curCommand = curConnection.CreateCommand();
            curCommand.CommandText = @"Insert into TestSP (SessionHead_EventId, SessionHead_Title, SessionHead_TypeId, SessionHead_Description, SessionHead_Status, SessionHead_Presenter, SessionHead_Champion, SessionHead_AnnounceDate, SessionHead_Objectives, SessionHead_LaunchDate, SessionHead_Notes, SessionHead_Schedule, SessionHead_SpecialNeeds, SessionHead_Equipment, SessionHead_CDA) Values (@a,@b,@c,@d,@e,@f,@g,@h,@i,@j,@k,@l,@m,@n,@o)";
            for (int j = 0; j < 15; j++)
            {
                param = new SqlParameter();
                str = "@";
                str += (char)('a' + j);
                param.ParameterName = str;
                param.SqlDbType = SqlDbType.VarChar;
                param.Value = DtSet.Tables[0].Rows[i][j];
                curCommand.Parameters.Add(param);
            }
            Label1.Text = "THE EXCEL DATE HAS SUCCESSFULLY BEEN SENT TO THE DATABASE";
            curCommand.ExecuteNonQuery();
            curCommand.CommandText = "UPDATE TestSP SET SessionHead_TypeId = ( SELECT SessionType.SessionType_Id FROM SessionType WHERE SessionType.SessionType_Title = TestSP.SessionHead_TypeId) WHERE EXISTS ( SELECT SessionType.SessionType_Id FROM SessionType WHERE SessionType.SessionType_Title = TestSP.SessionHead_TypeId)"; 
//****Can I add a statement here stating that if a NULL value is returned, to give me an error message on the website?****
        curCommand.ExecuteNonQuery();
        }

        MyConnection.Close();
        curConnection.Close();
    }
    catch (Exception ex)
    {
        //Response.Write(ex.ToString());
        Label1.Text = ex.Message;
        Label2.Text = ex.Message; 
    }

}

任何帮助将不胜感激！！