if not exists (select 1 from  sysobjects where  id = object_id('Table1')             and   type = 'U')
begin
 create table Table1 (
    id  int NOT NULL identity(1,1),
    .....
    constraint PK_Table1 primary key  (id)
 );
 end;

unit Unit2;

interface

uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs, StdCtrls, DB, ADODB;

type
 TForm2 = class(TForm)
   ADOConnection1: TADOConnection;
   ADOCommand1: TADOCommand;
   ADODataSet1: TADODataSet;
   Button1: TButton;
   Button2: TButton;
   Label1: TLabel;
   procedure FormCreate(Sender: TObject);
   procedure Button1Click(Sender: TObject);
   procedure Button2Click(Sender: TObject);
 private
   { Private declarations }
 public
   { Public declarations }
 end;

var
 Form2: TForm2;

implementation

{$R *.dfm}

procedure TForm2.Button1Click(Sender: TObject);
var
 ss : string;
begin
 ss := 'Select x=count(*) from test_table';
 try
  ADODataSet1.CommandText := ss;
  ADODataSet1.Open;
  Label1.Caption := ADODataSet1.FieldByName('X').AsString;
 finally
   ADODataSet1.Close;
 end;
end;

procedure TForm2.Button2Click(Sender: TObject);
var
 ss : string;
begin
 ss := 'if not exists (select 1 from sysobjects where id = object_id(''test_table'') and   type = ''U'') ' +
    'begin  create table test_table (id  int NOT NULL identity(1,1)) end';
 ADOCommand1.CommandText := ss;
 ADOCommand1.Execute;
end;

procedure TForm2.FormCreate(Sender: TObject);
begin
 ADOConnection1.Connected := True;
end;

end.