He is one of those people who promise more than can be done.

He is one of those people who promise more than can be done.
也可以变成主动语态的：He is one of those people who promise more things than they do.
好,现在来回答你的问题.He drank more wine than was good for him and got drunk
.He drank more wine than was good for him (他酒喝得太多,超出该喝的范围)
than在你的句子里面是连接词也是从句的主语,在我的句子里面也是如此.
结构是：-- - -比较级 than 谓语（+其他成分） .
又如：
1 Here in my bedroom there are more books than are needed for my school work.
2 Every day I do more homework than is good for my health.
现在,你会了吗?祝你学习天天向上.