如何在不打开数据集的情况下添加所有字段?

FieldDefs.Update 并从 FieldDefs 列表。

uses
  FIBDatabase, FIBDataSet, Dialogs;

...

var
  Db : TFIBDataBase;
  Tr : TFIBTransaction;
  Dst : TFIBDataSet;
  I : integer;
begin
  //connection
  Db := TFIBDatabase.Create(Self);
  Db.ConnectParams.UserName := 'SYSDBA';
  Db.ConnectParams.Password := 'masterkey';
  Db.DatabaseName := 'localhost:mydatabase.fdb';
  Db.SQLDialect := 3;
  Db.Connected := True;

  //transaction
  Tr := TFIBTransaction.Create(Self);
  Tr.DefaultDatabase := Db;
  Tr.Active := True;

  //dataset
  Dst := TFIBDataSet.Create(Self);
  Dst.Database := Db;
  Dst.Transaction := Tr;
  Dst.SelectSQL.Text := 'SELECT * FROM rdb$database';

  //create fields
  Dst.FieldDefs.Update();
  for I := 0 to Dst.FieldDefs.Count - 1 do
    Dst.FieldDefs[I].CreateField(Dst);

  ShowMessage(IntToStr(Dst.FieldCount));
end;