postgresql - 如何创建接受 NULL 的域？

Question

我似乎无法弄清楚如何获得 custom domain接受 NULL 值。请注意，对于狗屎和傻笑，我已经尝试了许多不同的方法:

DROP SCHEMA census CASCADE;
CREATE SCHEMA census;
-- FIRST FOUR METHODS: NULL before CHECK, in CHECK, and NULL after CHECK
CREATE DOMAIN census.sex AS text NULL CHECK ( VALUE IN ('M', 'F', 'NULL') OR VALUE IS NULL ) NULL;
CREATE TABLE census.names (
  name       text
  , freq     int
  , cumfreq  float
  , rank     float
  , is_last  bool
  , sex      census.sex NULL -- fourth way
  , PRIMARY KEY ( is_last, sex, name )
);

但是，仍然没有运气......

# \d census.names;
          Table "census.names"
 Column  |       Type       | Modifiers 
---------+------------------+-----------
 name    | text             | not null
 freq    | integer          | 
 cumfreq | double precision | 
 rank    | double precision | 
 is_last | boolean          | not null
 sex     | census.sex       | not null
Indexes:
    "names_pkey" PRIMARY KEY, btree (is_last, sex, name)

更有趣的是，the docs说

NULL

Values of this domain are allowed to be null. This is the default.

This clause is only intended for compatibility with nonstandard SQL databases. Its use is discouraged in new applications.

没有子句它仍然显示 NOT NULL。

$ psql --version
psql (PostgreSQL) 9.1.1
contains support for command-line editing

Answer 1

像往常一样:

1. 在 StackOverflow 上发布一个描述性问题
2. 将链接粘贴到 irc://irc.freenode.net/#postgresql
3. 让专家在几秒钟内回答问题。

11:17 < RhodiumToad> EvanCarroll: it's the primary key that does it - all columns of a primary key are not null

他什么都知道。