SELECT v,  median_filter(v::double precision, 5) over() FROM generate_series(1, 10) as t(v);
 v  | median_filter 
----+---------------
  1 |             1
  2 |             2
  3 |             3
  4 |             4
  5 |             5
  6 |             6
  7 |             7
  8 |             8
  9 |             8
 10 |             8
(10 rows)

SELECT v,  median_filter(v, 3) over() FROM (VALUES (1), (1.1), (0.9), (1.1), (0.95), (2.1), (1.95), (2.0), (2.05), (3.11), (2.99), (3.05), (3.0)) as t(v);
  v   | median_filter 
------+---------------
    1 |             1
  1.1 |             1
  0.9 |           1.1
  1.1 |          0.95
 0.95 |           1.1
  2.1 |          1.95
 1.95 |             2
  2.0 |             2
 2.05 |          2.05
 3.11 |          2.99
 2.99 |          3.05
 3.05 |             3
  3.0 |             3
(13 rows)

SELECT v,  median_filter(v, 3) over() FROM (VALUES (1), (1.1)) as t(v);
  v  | median_filter 
-----+---------------
   1 |             1
 1.1 |             1
(2 rows)

SELECT v,  median_filter(v::double precision, 3) over() FROM (VALUES (NULL), (NULL), (NULL)) as t(v);
 v | median_filter 
---+---------------
   |              
   |              
   |              
(3 rows)