"That book which is beside the new tv is long."
Translation:Az a könyv hosszú, amelyik az új televízió mellett van.
Vvsey talks a lot obut it here.
Summed up, you usually do not use ami with named nouns, but rather in constructions like "Arról beszélek, amit gondolok" - I talk about what I think. (Note how you cannot say here "I talk about which I think." Deutsch: "Ich sage, was ich denke" und nicht "Ich sage, welches ich denke.")
Here you're talking about a certain book, so you'll have to use amelyik - which. "The book which is next to the TV" - "Das Buch, welches neben dem Fernseher ist"
Whether you can swap the "that" for "which" might really help in this regard, hmm.
Nab, you're using van to describe the intrinsic quality (the size of the book), and no van to describe the extrinstic quality (the location of the book). It needs to be the other way around:
- Az a könyv hosszú. - The book is long. (no van)
- A könyv az új televízió mellett van. - The book is next to the TV. (van is used)
- Az a könyv, amelyik az új televízió mellett van, hosszú.
It's less about the word order, but more about which clause you put the van in. That's why using commas is so important in Hungarian: it lets you see what words are part of which concept. The van has to go into the same clause as mellett, since we need van to describe a location. So van and mellett cannot be separated by a single comma. On the other side, hosszú cannot be in the same clause as van, so they need to be separated by a comma.
You have the sentence "Az a könyv hosszú" as the basic statement of the sentence, and you're inserting a relative clause here in order to describe the book more precisely. But the relative clause must not leak words, which means that when you erase everything that's framed by commas, the base sentence must still be "Az a könyv hosszú", without any stray van.
- Az a könyv,
amelyik a televízió mellett van, hosszú.