All what的句子用法?

all what you need (錯)
all that you need (可以)
all you need (最好)

all what you need 是錯的，因為 all 在這裡是代名詞，可以說是代替了 all the things，所以後面只能加 that，不能用 what。

不過在實際使用上， all you need 比 all that you need 順口，更常用。以文法解說，need 是及物動詞，that 是 need 的受詞，所以屬於受格，而關係代名詞受格是可以省略的，所以 all that you need = all you need。

" All what you need" represents a subject only besides that should have its predicate, object or complement, i.e. All what you need is to buy a book.
The same case of "All the things that you need" and that will be completed as ;All the things that you need is to buy a book.
Yip