uses
SynCommons, SynDB, SynOleDB;

procedure TForm1.DataToJsonClick(Sender: TObject);
var
  Conn: TOleDBMSSQLConnectionProperties;
  strSql: string;
  rows: ISQLDBRows;
  strStream: TStringStream;
begin
  Conn := TOleDBMSSQLConnectionProperties.Create('127.0.0.1', 'Northwind', 'sa', 'Sa123');
  strSql := 'SELECT EmployeeID,LastName,FirstName,Title FROM Employees';
  strStream:=TStringStream.Create('',TEncoding.UTF8);
  try
    rows := Conn.ExecuteInlined(strSql, True);
    rows.FetchAllToJSON(strStream, True);
    Memo1.Text := strStream.DataString;
  finally
    strStream.Free;
  end;
end;