Can Any body discuss details of this Query Plan

pmdummy=# explain SELECT projectid FROM tblPermissions
pmdummy-# INNER JOIN tempaccountid ON tempaccountid.accid = tblPermissions.
countid
pmdummy-# WHERE tblPermissions.topid = 3915;

1. tempaccountid (accid integer) no indexe or no primary key
Number of Records 10
2. tblPermissions (accountid integer, raccountid integer, topid integer)
primary key(accountid, raccountid)
Number of Records appoximately 70,0000

Before indexing on tblpermissions (topid) i got query plan as

NOTICE: QUERY PLAN:

Hash Join (cost=22.51..47.83 rows=25 width=12)
-> Seq Scan on tempaccountid (cost=0.00..20.00 rows=1000 width=4)
-> Hash (cost=22.50..22.50 rows=5 width=8)
-> Seq Scan on tblpermissions (cost=0.00..22.50 rows=5 width=8)

EXPLAIN

After indexing on tblpermissions (topid) i got query plan as

NOTICE: QUERY PLAN:

Merge Join (cost=1345.76..1375.89 rows=2126 width=12)
-> Sort (cost=1275.93..1275.93 rows=425 width=8)
-> Index Scan using idx_tblpermissions_topid on tblpermissions
(cost=0
.00..1257.37 rows=425 width=8)
-> Sort (cost=69.83..69.83 rows=1000 width=4)
-> Seq Scan on tempaccountid (cost=0.00..20.00 rows=1000 width=4)

EXPLAIN

But I could not under stand this statistics. Can any body explain above.

Thanks to all seniors and gurus,

Sreedhar

"Faith, faith, faith in ourselves, faith, faith in God, this is the secret
of greatness.
If you have faith in all the three hundred and thirty millions of your
mythological gods,
and in all the gods which foreigners have now and again introduced into your
midst,
and still have no faith in yourselves, there is no salvation for you. "
(III. 190)