oracle - SQL - Joining multiple tables? -

i'm trying join multiple tables create list of purchase orders total cost. have tried following select statement returns error of "'oa'.'aircraft_code' invalid identifier"

select al.airline_code “airline code”,      po.purchase_order_no “order number”,     ac.aircraft_code “aircraft code”,     oa.aircraft_quantity “quantity of aircraft ordered”,     sum(oa.aircraft_quantity * ac.aircraft_price) “order total” aircraft ac, airline al, ordered_aircraft oa, purchase_order po     join airline al on po.airline_code = al.airline_code     join aircraft ac on oa.aircraft_code = ac.aircraft_code     join purchase_order po on oa.purchase_order_no = po.purchase_order_no group po.purchase_order_no order al.airline_code asc; 

the database structure follows:

aircraft

 name                                      null?    type  ----------------------------------------- -------- ----------------------------   aircraft_code                             not null varchar2(5 char)  aircraft_type                             not null varchar2(30 char)  aircraft_price                            not null number(11,2) 

airline

 name                                      null?    type  ----------------------------------------- -------- ----------------------------   airline_code                              not null varchar2(4 char)  airline_name                              not null varchar2(20 char)  airline_address                           not null varchar2(100 char)  airline_city                              not null varchar2(20 char)  airline_country                           not null varchar2(20 char) 

ordered_aircraft;

 name                                      null?    type  ----------------------------------------- -------- ----------------------------   purchase_order_no                         not null number(3)  aircraft_code                             not null varchar2(5 char)  aircraft_quantity                         not null number(2) 

purchase_order

 name                                      null?    type  ----------------------------------------- -------- ----------------------------   purchase_order_no                         not null number(3)  airline_code                                       varchar2(4 char)  purchase_order_date                       not null date 

any great. thank you.

take tables joining out of list after from:

select      al.airline_code “airline code”,      po.purchase_order_no “order number”,      ac.aircraft_code “aircraft code”,      oa.aircraft_quantity “quantity of aircraft ordered”,      sum(oa.aircraft_quantity * ac.aircraft_price) “order total” ordered_aircraft oa   /*  , airline al, ordered_aircraft oa, purchase_order po */   <--- join purchase_order po     on oa.purchase_order_no = po.purchase_order_no join airline al      on po.airline_code = al.airline_code join aircraft ac     on ac.aircraft_code = oa.aircraft_code group po.purchase_order_no order al.airline_code asc; 

using comma-separated list of tables different join syntax. if using join there's no need reference them again.