How can i query the last data from 3 tables - postgresql

Question

now i have 3 tables, for example A,B,C
the relation between them is A onetomany B, B onetomany C.
C is a table saved photos
now i want get data from A, but only the last photo each A.
the colomns maybe like this:
table a:
id a_msg
a1 msg in a
a2 msg in a
a3 msg in a
table b:
id b_msg a_id
b1 some data in b a1
b2 some data in b a1
b3 some data in b a2
b4 some data in b a3
table c:
id url createdate c_msg b_id
c1 /file/1.jpg 2014-12-01 06:55:54.600 some data in c b1
c2 /file/2.jpg 2014-12-01 06:55:54.601 some data in c b1
c3 /file/3.jpg 2014-12-01 06:55:54.602 some data in c b1
c4 /file/4.jpg 2014-12-01 06:55:54.603 some data in c b2
c5 /file/5.jpg 2014-12-01 06:55:54.604 some data in c b2
c6 /file/6.jpg 2014-12-01 06:55:54.605 some data in c b3
the result i want get
c_id url createdate c_msg b_msg b_id a_msg a_id
c6 /file/6.jpg 2014-12-01 06:55:54.605 some data in c some data in b b3 msg in a a1
c5 /file/5.jpg 2014-12-01 06:55:54.604 some data in c some data in b b2 msg in a a1
Sorry ,i don't know how to use tool to describle the table,hope you can easily understand what i mean.
if my description is not clear enough,i will edit the question,thank you if anyone can help me

Answer 1

Consider the following as an example :
create table table_a (id int,a_msg text);
create table table_b (id int,b_msg text,a_id int);
create table table_c (id int,url text,createdate timestamp with time zone,c_msg text ,b_id int);
and the data
insert into table_a values (1,'msg in table_a')
,(2,'2nd msg in table_a')
,(3,'3rd msg in table_a');
insert into table_b values (20,'msg in table_b',1)
,(21,'2nd msg in table_b',2)
,(22,'3rd msg in table_b',3);
insert into table_c values (30,'url','2014-12-01 06:55:54.600','msg in table_c',20)
,(31,'url 1','2014-12-01 06:55:54.604','2nd msg in table_c',21)
,(32,'url 2','2014-12-01 06:55:54.605','3rd msg in table_c',22);
to get the result you need to use INNER JOIN and to get the last two data use order by createdate desc limit 2
select c.id,c.url
,c.createdate
,c.c_msg,b.b_msg
,b.id bi_id,a.a_msg
,a.id a_id
from
table_c c inner join table_b b on c.b_id=b.id /* to get data from table_b */
inner join table_a a on b.a_id=a.id /* to get data from table_a */
order by createdate desc limit 2 /* DESC will sort from the highest date time values and LIMIT 2 will return two rows */
>SQLFIDDLE DEMO WITH OP'S DATA