第二个选项意味着你的reader在创建后如果出现异常会关闭，所以首选.

The second option means your reader will be closed in the event of an exception after it has been created, so it is preferred.

它被编译器有效地转换为:

It is effectively transformed by the compiler to:

SqlDataReader reader = command.ExecuteReader();
try
{
    ....
}
finally
{
  if (reader != null)
      ((IDisposable)reader).Dispose();
}

有关详细信息，请参阅 MSDN.

See MSDN for more info.