sql - Implementing NULLS FIRST in Amazon Redshift -

i using sum window function row number, similar query -

select field_a,        sum(1) on (partition field_b order field_c asc rows unbounded preceding) row_number test_table     order row_number; 

the problem if field_c null value, appears @ end. want @ beginning, null value treated smaller other values. in oracle, done providing nulls first argument, not supported in redshift. how implement in redshift ?

i want [null] @ beginning, null value treated smaller other values.

use expression

field_c not null 

as first order by item. evaluates ...
false .. if null
true .. if not null.

and false (0) sorts before true (1). works data type , possible distribution of values.

select field_a,        row_number() on (partition field_b                           order field_c not null, field_c) row_number   test_table order  row_number;