an item or not?

Hi, I have this table : prestito where there is the column "id_libro" that
contains all the book that are not in my house (with some other infos).
But I have the table
"libro" that contains the data about every books in my house. Now I have a
query /via web interface with php) that give me infos about all books and
if the book
is in the house I put an
button in the page (via php script). Now, for this choice (button or not
button) it is better a column call "id_utente" in the "libro" table or a
select from the "prestito" table foreach book ?

exscume me for my bad english

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