order by null

gistfile1.sql

test=# create table nullorder (created_at timestamp);
CREATE TABLE
test=# insert into nullorder (created_at) values (null), (null), ('1999-01-08 04:05:06'), ('1999-11-08 04:05:06'), (null);
INSERT 0 5

test=# select * from nullorder;
     created_at      
---------------------
 
 
 1999-01-08 04:05:06
 1999-11-08 04:05:06
 
(5 rows)

test=# select * from nullorder order by created_at is null DESC, created_at;
     created_at      
---------------------
 
 
 
 1999-01-08 04:05:06
 1999-11-08 04:05:06
(5 rows)

test=# select * from nullorder order by created_at = null DESC, created_at;
     created_at      
---------------------
 1999-01-08 04:05:06
 1999-11-08 04:05:06
 
 
 
(5 rows)

test=# select * from nullorder order by isnull(created_at) DESC, created_at;
ERROR:  function isnull(timestamp without time zone) does not exist
LINE 1: select * from nullorder order by isnull(created_at) DESC, cr...
                                         ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.