i have no idea that 是什么从句

Question

I have no idea when he will come back和I have no idea that he will come back有什么区别?
这两个句子都对吗？都是同位语从句吗？

Answer 1

I have no idea when he will come back------------我不知道他何时回来.
I have no idea that he will come back-----------他会回来?这一点我不知道.