postgresql – 对别名字段的Postgres整理

CREATE TABLE public_bodies
  ("id" int,"name" varchar(46))
;

INSERT INTO public_bodies
  ("id","name")
VALUES
  (1,'Ytre Helgeland District Psychiatric Centre'),(2,'?fjord Municipality'),(3,'?stfold Hospital')
;

我想运行这个查询：

SELECT public_bodies.id,public_bodies.name AS display_name
FROM public_bodies
ORDER BY display_name COLLATE "en_US";

但我得到这个错误：

ERROR:  column "display_name" does not exist
LINE 3: ORDER BY display_name COLLATE "en_US";
                 ^

按表名排序可以正常工作：

SELECT public_bodies.id,public_bodies.name AS display_name
FROM public_bodies
ORDER BY public_bodies.name COLLATE "en_US";

--  id |        display_name
-- ----+--------------------------------------------
--   2 | ?fjord Municipality
--   3 | ?stfold Hospital
--   1 | Ytre Helgeland District Psychiatric Centre

在别名上订购也可以：

SELECT public_bodies.id,public_bodies.name AS display_name
FROM public_bodies
ORDER BY display_name;

--  id |        display_name
-- ----+--------------------------------------------
--   2 | ?fjord Municipality
--   3 | ?stfold Hospital
--   1 | Ytre Helgeland District Psychiatric Centre

在分配别名之前应用COLLATE有效,但我不明白为什么这与ORDER_BY之后的整理不同.

SELECT public_bodies.id,public_bodies.name COLLATE "en_US" AS display_name
FROM public_bodies
ORDER BY display_name;

--  id |        display_name
-- ----+--------------------------------------------
--   2 | ?fjord Municipality
--   3 | ?stfold Hospital
--   1 | Ytre Helgeland District Psychiatric Centre

Postgres版本：

SELECT version();
                                               version
-------------------------------------------------------------------------------------------------------------
 PostgreSQL 9.1.12 on x86_64-unknown-linux-gnu,compiled by gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3,64-bit

我在SQL小提琴上得到了相同的结果(Postgres 9.3).

为什么Postgres不能在别名字段上整理？