void SQLApp::Query()
{
	SqlBool where;
	SqlSet borrowed = Select(BOOK_ID).From(BORROW_RECORD).Where(IsNull(RETURNED));
	if(query.status == 1)
		where = ID != borrowed;
	if(query.status == 2)
		where = ID == borrowed;
	SqlBool bdate;
	if(!IsNull(query.borrowed_from))
		bdate = BORROWED >= ~query.borrowed_from;
	if(!IsNull(query.borrowed_to))
		bdate = bdate && BORROWED <= ~query.borrowed_to;
	if(!bdate.IsEmpty())
		where = where && ID == Select(BOOK_ID).From(BORROW_RECORD).Where(bdate);
	book.Query(where);
}