我认为这样比较好:

SELECT * FROM "comments" WHERE ("comments"."id" IN (1,3,2,4))
    ORDER BY  id=1 DESC, id=3 DESC, id=2 DESC, id=4 DESC

在Postgres 9.4或更高版本中，这是最简单和最快的:

SELECT c.*
FROM   comments c
JOIN   unnest('{1,3,2,4}'::int[]) WITH ORDINALITY t(id, ord) USING (id)
ORDER  BY t.ord;

WITH ORDINALITY was introduced with in Postgres 9.4. No need for a subquery, we can use the set-returning function like a table directly. (A.k.a. "table-function".) A string literal to hand in the array instead of an ARRAY constructor may be easier to implement with some clients. For convenience (optionally), copy the column name we are joining to ("id" in the example), so we can join with a short USING clause to only get a single instance of the join column in the result. Works with any input type. If your key column is of type text, provide something like '{foo,bar,baz}'::text[].

详细解释:

PostgreSQL unnest()与元素号

create sequence serial start 1;

select * from comments c
join (select unnest(ARRAY[1,3,2,4]) as id, nextval('serial') as id_sorter) x
on x.id = c.id
order by x.id_sorter;

drop sequence serial;

(编辑)

Unnest在8.3中还没有内置，但你可以自己创建一个(任何的美丽*):

create function unnest(anyarray) returns setof anyelement
language sql as
$$
    select $1[i] from generate_series(array_lower($1,1),array_upper($1,1)) i;
$$;

该函数可以在任何类型下工作:

select unnest(array['John','Paul','George','Ringo']) as beatle
select unnest(array[1,3,2,4]) as id

你可以很容易地使用(在PostgreSQL 8.2中引入)VALUES()，()。

语法是这样的:

select c.*
from comments c
join (
  values
    (1,1),
    (3,2),
    (2,3),
    (4,4)
) as x (id, ordering) on c.id = x.id
order by x.ordering

我认为这样比较好:

SELECT * FROM "comments" WHERE ("comments"."id" IN (1,3,2,4))
    ORDER BY  id=1 DESC, id=3 DESC, id=2 DESC, id=4 DESC

在Postgres 9.4中，这可以做得更短一些:

select c.*
from comments c
join (
  select *
  from unnest(array[43,47,42]) with ordinality
) as x (id, ordering) on c.id = x.id
order by x.ordering;

或者在没有派生表的情况下更加紧凑:

select c.*
from comments c
  join unnest(array[43,47,42]) with ordinality as x (id, ordering) 
    on c.id = x.id
order by x.ordering

无需手动为每个值分配/维护位置。

在Postgres 9.6中，可以使用array_position():

with x (id_list) as (
  values (array[42,48,43])
)
select c.*
from comments c, x
where id = any (x.id_list)
order by array_position(x.id_list, c.id);

使用CTE时，值列表只需要指定一次。如果这并不重要，也可以写成:

select c.*
from comments c
where id in (42,48,43)
order by array_position(array[42,48,43], c.id);