postgresql - 仅使用 SELECT 从 information_schema 中查找 Postgresql 中表的主键

Question

我正在使用以下查询来发现 (1) 主键列和 (2) 这些列是否具有来自 Postgresql 9.1 中的 information_schema 的默认值。

SELECT kcu.column_name, (c.column_default is not null) AS has_default 
FROM information_schema.key_column_usage kcu 
JOIN information_schema.table_constraints tc ON tc.constraint_name = kcu.constraint_name 
JOIN information_schema.columns c on c.column_name = kcu.column_name and c.table_name = kcu.table_name  
WHERE tc.constraint_type = 'PRIMARY KEY' AND kcu.table_name like :tablename

当以数据库所有者身份运行时它工作正常，但当我以“只读”用户身份运行它时(我需要在我的应用程序中这样做)，它不返回任何数据。一些研究表明问题出在 information.table_constraints View 上；来自文档:

The view table_constraints contains all constraints belonging to tables that the current user owns or has some non-SELECT privilege on.

那么为了检索 table_constraints，我的登录角色需要的不仅仅是表上的 SELECT？如果不授予登录角色写入权限，是否无法从 information_schema 获取信息？

Answer 1

使用 pg_* View 而不是 information_schema View 。
pg_* View 显示所有信息，而不管授予的权限。

试试这个查询:

select
    t.relname as table_name,
    i.relname as index_name,
    a.attname as column_name,
    d.adsrc   as default_value
from
    pg_class t
    join pg_attribute a on a.attrelid = t.oid
    join pg_index ix    on t.oid = ix.indrelid AND a.attnum = ANY(ix.indkey)
    join pg_class i     on i.oid = ix.indexrelid
    left join pg_attrdef d on d.adrelid = t.oid and d.adnum = a.attnum  
where
    t.relkind = 'r'
    and t.relname in ( 'aa', 'bb', 'cc' )
order by
    t.relname,
    i.relname,
    a.attnum;

查询结果示例:

create table aa(
  x int primary KEY
);

create table bb(
  x int default 1,
  constraint pk primary key ( x )
);

create table cc(
  x int default 20,
  y varchar(10) default 'something',
  constraint cc_pk primary key ( x, y )
);

 table_name | index_name | column_name |         default_value
------------+------------+-------------+--------------------------------
 aa         | aa_pkey    | x           |
 bb         | pk         | x           | 1
 cc         | cc_pk      | x           | 20
 cc         | cc_pk      | y           | 'something'::character varying