postgres=# \d test
     Table "public.test"
 Column |  Type   | Modifiers 
--------+---------+-----------
 bit    | boolean | 
 but    | integer | 

postgres=# select count(but) from test where bit;
 count 
-------
  1049
(1 row)

postgres=# explain select but from test where bit limit 1000;
                           QUERY PLAN                            
-----------------------------------------------------------------
 Limit  (cost=0.00..7451.00 rows=1000 width=4)
   ->  Seq Scan on test  (cost=0.00..15051.03 rows=2020 width=4)
         Filter: "bit"
(3 rows)