Database

create or replace view grouped_table as
select col2
      ,max(ID)
 from table
group by col2
;

select t.ID
      ,t.col2
      ,t.col3
  from table t
      ,grouped_table gt
 where t.id = gt.id

select t.ID
      ,t.col2
      ,t.col3
  from table t
      ,(  select col2
                ,max(ID) id
            from table
           group by col2
       ) gt
 where t.id = gt.id

select * from TT where id in (
  select max(id) from tt group by col2)

Table1 inner join Table2

Table2 inner join Table1

 
--  Connect.cs file.
public static void connectDB()
    {
        try
        {
                conn.ConnectionString = connection;
                conn.Open();
        }
        catch
        {
            //closeConnectDB();
        }
    }
    public static void closeConnectDB()
    {
        //conn.Dispose();
            conn.Close();
        //conn.Dispose();
    }
    public static int ExecuteQuery(string SQL)
    {
        try
        {
            connectDB();
            NpgsqlCommand cmd = new NpgsqlCommand(SQL, conn);
            return cmd.ExecuteNonQuery();
        }
        catch
        {
            closeConnectDB();
            return 0;
        }
        
    }
 
    public static DataSet SelectQuery(string SQL)
    {
        DataSet ds = new DataSet();
        try
        {
            connectDB();
            NpgsqlDataAdapter nDa = new NpgsqlDataAdapter(SQL, conn);
            
            nDa.Fill(ds);
            // closeConnectDB();
            return ds;
        }
        catch
        {
            closeConnectDB();
            return ds;
        }
        
    }

--- calling functions files.
try
                        {
                            string strTest = "Select * from abc where .. ";
                            DataSet ds1 = new DataSet();
                            ds1 = Connect.SelectQuery(strTest);
                            if (ds1.Tables[0].Rows.Count > 0)
                            {
                                
                            }
                            else
                            {
                                int kq = Connect.ExecuteQuery(strInsert);
                                if (kq > 0)
                                {
                                    int kk = Connect.ExecuteQuery(strUpdate);
                                    kk = Connect.ExecuteQuery(strUpdate2);
                                    
                                    strHTML = "OK";
                                }
                            }
                        }
                        catch
                        {
                            strHTML = "errors.";
                        }
                        finally
                        {
                            int kk = Connect.ExecuteQuery(strUpdate);
                            kk = Connect.ExecuteQuery(strUpdate2);
                           
                            strHTML += "-- Sub Finally";
                        }

messages wrote:

question is this a correct desgin for implementation or no

Bastard Programmer from Hell

Hamid. wrote:

I have almost like this problem I want to know do I need to normalization-rules no?

Bastard Programmer from Hell

messages wrote:

Do I need to Foreign key in Authors table or Book tables?