Postgresql: Ordering columns to match custom criteria

Question

I'm having trouble sorting the result of a query.

After executing this query:

SELECT id_doc_header, id_clasificacion_doc 
FROM cabecera_documento INNER JOIN tipo_doc USING (id_tipo_doc) 
 INNER JOIN clasificacion_documento USING (id_clasificacion_doc) 
WHERE finalizado = 'f' AND cod_exp = '10-APC-2013' AND id_clasificacion_doc in(2,3,4,5)
ORDER BY case when Id_clasificacion_doc = 5 THEN 5 when Id_clasificacion_doc = 3 THEN 3 
  when Id_clasificacion_doc = 2 THEN 2 when Id_clasificacion_doc = 4 THEN 4 END;

or this:

SELECT id_doc_header, id_clasificacion_doc 
FROM cabecera_documento INNER JOIN tipo_doc USING (id_tipo_doc) 
INNER JOIN clasificacion_documento USING (id_clasificacion_doc) 
WHERE finalizado = 'f' AND cod_exp = '10-APC-2013' 
AND id_clasificacion_doc in(2,3,4,5) 
ORDER BY id_clasificacion_doc = 5, id_clasificacion_doc = 3, id_clasificacion_doc = 2, id_clasificacion_doc = 4;

the result I get is:

 id_doc_header | id_clasificacion_doc 
---------------+----------------------
          1657 |                    2
          1658 |                    3
          1658 |                    2
          1661 |                    4
          1663 |                    4
          1665 |                    5

My question is: What can I do to get the results in the next order?

 id_doc_header | id_clasificacion_doc 
---------------+----------------------
          1665 |                    5
          1658 |                    3
          1657 |                    2
          1661 |                    4
          1663 |                    4

I'm using posgresql 9.1.

Thanks in advance.

Answer 1

Try being explicit about the order by:

order by (case when id_clasificacion_doc = 5 then 1
               when id_clasificacion_doc = 3 then 2
               when id_clasificacion_doc = 2 then 3
               when id_clasificacion_doc = 4 then 4
          end)

Answer 2

As @ruakh intimated:

AnimalsPriority (animal varchar, priority numeric)
cat, 2.0
dog, 1.0
moose, 1.1

Animals (animal varchar)
cat
dog
moose


select * from Animals A
inner join AnimalsPriority AP
on A.animal = AP.animal
order by AP.priority

If you "hard-code" the sort-order into the query you must change the query if the priority changes. Keeping the sort-priority as a kind of metadata is more flexible, and if you use a number with a decimal point you can always inject new values into the sort order without having to renumber everything.

Answer 3

I believe your latter example should work as so:

ORDER BY id_clasificacion_doc = 5 DESC,
         id_clasificacion_doc = 3 DESC,
         id_clasificacion_doc = 2 DESC,
         id_clasificacion_doc = 4 DESC;