Retrieving value in C# from oracle database

I dont know why but I'm getting an error trying to get the maximum integer value from a table in the oracle database: Here is the code:

开发者_C百科string oradb = "Data Source=";
            oradb = oradb + Login.db + ";";
            oradb = oradb + "User Id=" + Login.user;
            oradb = oradb + ";Password=" + Login.pass + ";";
            OracleConnection conn = new OracleConnection(oradb);
            conn.Open();
            string term = GetTerminal(terminal);
            string sql = "SELECT tallynumber from "+frmSchemas.schema + ".tallies" ;
             MessageBox.Show(sql);
            OracleCommand cmd = new OracleCommand(sql, conn);
            cmd.CommandType = CommandType.Text;
            OracleDataReader dr = cmd.ExecuteReader();
            MessageBox.Show("1");
            Int64 TallyNo = dr.GetInt32(0);  



      // lblTallyNo.Text = (TallyNo).ToString()

the returned value should be: 72332 if that is any relevance

You can try with the Following

        string sql = "SELECT max(tallynumber) from "+frmSchemas.schema + ".tallies" ;
         MessageBox.Show(sql);
        OracleCommand cmd = new OracleCommand(sql, conn);
        cmd.CommandType = CommandType.Text;
        OracleDataReader dr = cmd.ExecuteReader();
        MessageBox.Show("1");
        if (dr.Read())
        {
        Int64 TallyNo = dr.GetInt32(0); 
        }

EDIT:

if(dr.Read())
{
Int64 TallyNo = Convert.ToInt64(dr["tallynumber"].ToString());
}

You are missing a dr.Read(); before accessing the value:

OracleDataReader dr = cmd.ExecuteReader();
dr.Read();
Int64 TallyNo = dr.GetInt32(0);

If you want to find the max value from a table, the query should be

SELECT max(tallynumber) from ....

If you want to get the max, min etc values you should be calling ExecuteScalar() instead of ExecuteReader().

So you code could become

   string sql = "SELECT Max(tallynumber) from "+frmSchemas.schema + ".tallies";              MessageBox.Show(sql);             
    OracleCommand cmd = new OracleCommand(sql, conn);             
    cmd.CommandType = CommandType.Text;             
    object val = cmd.ExecuteScalar();
int res = int.MinValue;             
    //MessageBox.Show("1");
  if(int.TryParse(val.ToString(), out res)) 
    Int64 TallyNo = res;