Question

Many people in the world have a dream, that one day they could come to China and visit Beijing.

逗号后面不是不能用that吗？

Answer 1

Many people in the world have a dream which one day they could come to China and visit Beijing.
用that没那么好，用which更好。
世上的很多人有个一天他们来中国参观北京的梦想。

Answer 2

对啊，这里的关系代词that前面一般是不用逗号的。

Answer 3

这里的逗号是不规范的，用法完全可以省略不用。这样that从句成为dream的同位语。
翻译:
世界上有很多人梦想有朝一日能去中国游览长城。

Answer 4

对的，逗号后面不可以用that。

Answer 5

英语很简单又直白，没有任何规定that 不能在逗号前或后。