2 rows expected on a primary key

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Hi all,
I'm running a 7.4.x engine and I'm seeing in a explain analyze:

- -> Hash (cost=4.00..4.00 rows=2 width=16) (actual time=30.542..30.542 rows=0 loops=1)
-> Index Scan using user_login_login_key on user_login ul (cost=0.00..4.00 rows=2 width=16) (actual time=30.482..30.490 rows=1 loops=1)
Index Cond: ((login)::text = 'Zoneon'::text)

why postgres perform an extimation of 2 rows knowing that column it's a primary key ?

If I do an explain analyze directly on the table I get:

# explain analyze select * from user_login where login = 'Zoneon';
QUERY PLAN
- ----------------------------------------------------------------------------------------------------------------------------------
Index Scan using user_login_login_key on user_login (cost=0.00..4.00 rows=1 width=16) (actual time=0.050..0.052 rows=1 loops=1)
Index Cond: ((login)::text = 'Zoneon'::text)
Total runtime: 4.627 ms
(3 rows)

btw, is it normal that cast ?

Regards
Gaetano Mendola

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