Searching Criteria to find out the friends of friend

Question

Senior DBA'S
i need to make database where i need to search the person from the current user. Current user can have many friends in his friend list but whom current user searching may be he is not a friend of current user and find out how current user known to that person. Like a friend's Chain.
Suppose that i m Aman finding out "San". my friends are Abhi, johan, satish etc,
further abhi's friend is "San" and
Satish is friend of Mohan, Mohan further friend of Sanju and Sanju will be friend of "San"
so "Aman" known to "San" by two ways one way by Abhi and 2nd way by Satish. Like link will be
Aman -> Abhi -> San
Aman -> Satish -> Mohan -> Sanju -> San
which way i am asking that is used by linkedin (www.linkedin.com)
So, Please tell me what best searching criteria will be used to achieve the target with performance because Records can be in billions.

Answer 1

should be like that
create table PALS (
pal_id number primary key ,
Name varchar2(100));
drop table FRIENDS;
create table FRIENDS(
pal_id number ,
friend_id number ,
primary key(pal_id , friend_id),
foreign key (pal_id) references PALS(pal_id),
foreign key (friend_id) references PALS(pal_id)
insert into pals values (1,'A');
insert into pals values (2,'B');
insert into pals values (3,'C');
insert into pals values (4,'D');
insert into pals values (5,'E');
insert into pals values (6,'F');
insert into pals values (7,'G');
insert into friends values (1,2);
insert into friends values (1,3);
insert into friends values (2,5);
insert into friends values (5,7);
insert into friends values (3,4);
insert into friends values (4,6);
insert into friends values (6,7);
commit;
-- find leads to G
with PF as (
select p.pal_id, p.name, f.friend_id, pf.name friend
from pals p
join friends f on p.pal_id=f.pal_id
join pals pf on pf.pal_id=f.friend_id)
select level, pf.name, pf.friend
from PF
connect by prior pal_id = friend_id start with friend='G';
     LEVEL NAME       FRIEND  
         1 E          G         
         2 B          E         
         1 F          G         
         2 D          F         
         3 C          D          then you have to unwrap it in application.
May be it is possible in SQL also.
Edited by: Mark Malakanov (user11181920) on Jan 10, 2013 10:56 AM
I've found how to do it
with PF as (
select p.pal_id, p.name, f.friend_id, pf.name friend
from pals p
join friends f on p.pal_id=f.pal_id
join pals pf on pf.pal_id=f.friend_id),
W as (
select level, pf.name, pf.friend,
CONNECT_BY_ROOT name R,
SYS_CONNECT_BY_PATH(friend,' -> ') P,
CONNECT_BY_ISLEAF IsLeaf
from PF
connect by pal_id = prior friend_id start with name='A'
select R || P P from W where IsLeaf=1 and friend='G';
P                                                                             
A -> B -> E -> G                                                                
A -> C -> D -> F -> G  Edited by: Mark Malakanov (user11181920) on Jan 10, 2013 11:28 AM
Edited by: Mark Malakanov (user11181920) on Jan 10, 2013 11:33 AM
So, Please tell me what best searching criteria will be used to achieve the target with performance because Records can be in billions.create index PALS_NAME on PALS(NAME);
or use PAL_ID in
connect by pal_id = prior friend_id start with PAL_ID=1
Edited by: Mark Malakanov (user11181920) on Jan 10, 2013 11:42 AM
Edited by: Mark Malakanov (user11181920) on Jan 10, 2013 11:44 AM