col1        col2        col3        col4
a           b           (null)      c
a           b           (null)      c
a           (null)      (null)      c
(null)      b           (null)      (null)
a           b           (null)      (null)
a           b           (null)      (null)

column_name         count_of_non_null
col1                5
col2                5
col3                0
col4                3