what is TADOQuery component for Delphi?

TADOQuery component is aimed at execution of SQL-commands. It can be considered as an analog of TSQLQuery component from dbExpress. Connection to the database is set via Connection or ConnectionString properties. Query text is written to SQL property. If a query returns the dataset one should use Open() method or Active=true property. If a query does not return the dataset, it shall be run using ExecSQL method. ExecSQL returns the number of records processed during a query running. The same value is contained in RowsAffected property.

What is TADOConnection in Delphi

TADOConnection component connects to the data storage. TADOConnection resembles TSQLConnection component. The difference between them is that when working with TSQLConnection connection parameters are set via ConnectionName, DriverName and Paramsproperties. In TADOConnection all connection parameters are set via ConnectionString property. Moreover, it is possible to specify file name with connection parameters as a connection string in TADOConnection.

Connection String with Firebird database in Delphi XE2

procedure TForm1.Button1Click(Sender: TObject);
var 
 Conn: TSQLConnection;
begin
  Conn := TSQLConnection.Create(Self);
  try
    Conn.DriverName := 'Provider=MSDASQL.1; '+
                       'Persist Security Info=False; '+
                       'Data Source=DataBaseName; '+
                       'Initial Catalog=DataBaseName';'; 
    Conn.Params.Add('User_Name=SYSDBA');
    Conn.Params.Add('Password=masterkey');

    // Replace the dbname in the next line with the
    // value obtained at runtime, as  in
    // Conn.Params.Add('Database=' + YourNewPathAndDBName);
    Conn.Params.Add('Database=D:\FolderName\DataBaseName.fdb');

    Conn.Open;
    if Conn.Connected then
      ShowMessage('Connection successfully made to DB');
  finally
    Conn.Free;
  end;
end;

Q :- What is the difference between the SuperServer, classic and embedded servers ?

Ans:-SuperServer is a single-process multi-threaded server (like Apache on Windows, for example) Classic is a multi-process single-threade server - things are synced via a separate lock manager process Embedded is a DLL you hook up to your application and work with database file directly

SuperServer is good for OLTP, lot of users, etc. Classic is good for OLAP or few users running heavy queries. Embedded is good for desktop apps.

You should install and use SuperServer while developing, since embedded only allows one connection at a time, so you cannot access the database from your application and administration tool at the same time. Later, you can deploy using any of those 3 architectures.