查询语料库发现，goodbye是使用频率最高的，good-bye次之，good bye最少。

这三者有没有句法差异呢？我们可以把它们的功能大致归纳成如下几类：(1)用于直接引语；(2)用于说话动词（say, tell等）的宾语；(3)用于非说话动词（kiss, wave等）的宾语；(4)在其它结构中作名词。

观察语料可发现，三种结构皆可用于四种功能：

"I'll see you later, Simon. Goodbye, Enola."

Did you come to say goodbye?

She waved goodbye, smiled, and left for what I thought was work.

Then, without a goodbye, they hobbled out from underneath the tent.

"Mom, sorry, gotta go right now, good-bye," she said, and hung up.

It would at least give him a chance to say good-bye.

I waved good-bye until they were gone.

He wouldn't just leave out without a good-bye.

"Good bye, Professor, and good luck."

My father's words echoed in my head as I stood in the Augusta station and said good bye to Horace Tabor on a bitterly cold spring morning.

The Rookie smiles and Wendy waves good bye.

I leave a good bye message at the dairy and arrive by train in Davos five hours later.