public ArrayList querryAllBooks(){
		String querry = "select * from book;";
		
		ArrayList al = null;
		DBManager dbm = null;
		Connection conn = null;
		Statement stmt = null;
		ResultSet rs= null;
		
		try{
			dbm = new DBManager();
			conn = dbm.getConnection();
			stmt = conn.createStatement();
			rs = stmt.executeQuery(querry);
			al = new ArrayList();
			
			while(rs.next()){
				Book bk = new Book();
				bk.setId(rs.getInt(1));
				bk.setName(rs.getString(2));
				bk.setAuthor(rs.getString(3));
				bk.setBookman(rs.getString(4));
				bk.setPrice(rs.getFloat(5));
				bk.setCategoryId(rs.getInt(6));
				bk.setIntroduction(rs.getString(7));
				bk.setOnSaleDate(rs.getDate(8));
				bk.setOnSaleNum(rs.getInt(9));
				bk.setRemainNum(rs.getInt(10));		
				
				al.add(bk);
			}
			
			return al;
			
		}catch(Exception e){
			e.printStackTrace();
		}finally{
			dbm.closeAll(rs, stmt, conn);
		}
		
		return al;
	}