Datagridview show only last record although I have more rows when compare currentreading excel and invoice table

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ADO.NET

C#5.0

OleDb

.NET4.6

Problem

Datagridview show only last record although I have more rows when currentreading excel is less than currentreading invoice table .

wrong result in else statement of btn_import click inside for loop count
I need to modify code in else to accept list not show only one record .

Details

I have excelsheet as following :

unitcode CurrentReading
12 2000
14 4500

and I have table Invoice in database in sql server 2012 has following fields

serial unitcode CurrentReading year month
1 12 1000 2018 3
3 14 5000 2018 3

so that how to display unit code 14 in datagridview .

Actually what i need is when currentreading for unit code in excel sheet is less than currentreading in table invoice display the values in datagridview . the formula as following

btn import that import from excel

btn_import click
{
for (int i = 0; i < dt.Rows.Count; i++)                               
{
  System.Data.DataTable dt = new System.Data.DataTable();
  dt = Showdataprint();
decimal LastMeterReading = ConvertToDecimal(GetLastReading(dt.Rows[i]["UnitCode"].ToString()));
 if (!string.IsNullOrEmpty(dt.Rows[i]["CurrentMeterReading"].ToString()) && ConvertToDecimal(dt.Rows[i]["CurrentMeterReading"]) > 0 && ConvertToDecimal(dt.Rows[i]["CurrentMeterReading"]) > ConvertToDecimal(LastMeterReading))
  {
//insert to table invoice
  }
else
{
System.Data.DataTable dtErrorRows = new DataTable();
 DataView  dv2 = new DataView(dt);
 dv2.RowFilter = "(CurrentMeterReading < " + LastMeterReading + ")" + "and" + "(UnitCode = " + Utilities.ObjectConverter.ConvertToInteger(dt.Rows[i]["UnitCode"]) + ")";
 dv2.RowStateFilter = DataViewRowState.CurrentRows;
 int a = dv2.Count;
 if (dv2.Count > 0)
   {
dtErrorRows = dv2.ToTable();
   }                                       
}
}
Grid.DataSource = dtErrorRows;
}
 function get data from excel
public System.Data.DataTable Showdataprint()
        {
            string connectionString = string.Format("Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties=\"Excel 12.0 Xml;HDR=YES;IMEX=1\";", txtpath.Text);

            OleDbConnection con = new OleDbConnection(connectionString);


            con.Open();

            string str = @"SELECT    [UnitCode],[CurrentMeterReading] FROM  [Sheet5$] ";
            OleDbCommand com = new OleDbCommand();
            com = new OleDbCommand(str, con);
            OleDbDataAdapter oledbda = new OleDbDataAdapter();
        oledbda = new OleDbDataAdapter(com);
        DataSet ds = new DataSet();
        ds = new DataSet();
        oledbda.Fill(ds, "[Sheet5$]");
        con.Close();
        System.Data.DataTable dt = new System.Data.DataTable();
        dt = ds.Tables["[Sheet5$]"];
        return dt;


    }

for selecting currentreading from Invoice Table :

private decimal GetLastReading(string UnitCode)
        {
            string sqlquery = "";
            sqlquery = @"select isnull((select top 1 CurrentMeterReading from WAHInvoice where UnitCode=" + UnitCode + " order by year , Serial desc),0)";

            object nullableValue = DataAccess.ExecuteScalar(sqlquery);
            decimal myValue;
            if (nullableValue == null || nullableValue == DBNull.Value)
            {
                myValue = 0;
            }
            else
            {

                decimal.TryParse(nullableValue.ToString(), out myValue);
            }

            return Utilities.ObjectConverter.ConvertToDecimal(DataAccess.ExecuteScalar(sqlquery));
    }

Expected Result in datagridview

unitcode CurrentReading

14 4500

What I have tried:

Datagridview show only last record although I have more rows when compare currentreading excel and invoice table