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..30.490rows=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=1loops=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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