What does explain show ?

Hi all,

I have a question about "explain" output.
Could someone teach me ?

Let a and b tables such that

create table a (
int4 pkey primary key,
....
);

create table b (
int4 key1,
int2 key2,
....,
primary key (key1,key2)
);

Table a has 15905 rows and table b has 25905 rows.

For the following query

select a.pkey, b.key2 from a, b
where b.key1 = 1369
and a.pkey = b.key1;

"explain" shows

NOTICE: QUERY PLAN:

Nested Loop (cost=6.19 rows=3 width=10)
-> Index Scan using b_pkey on b on b (cost=2.09 rows=2 width=6)
-> Index Scan using a_pkey on a on a (cost=2.05 rows=15905 width=4)

What does "rows=15905" of InnerPlan mean ?
Is "rows=3" of Nested Loop irrelevant to "rows=15905" ?

Regards.

Hiroshi Inoue
Inoue(at)tpf(dot)co(dot)jp