从PostgreSQL数据库中检索注释

Question

我正在Postgres数据库上运行一个项目，需要检索数据库中列的注释，以用作表格标题等。我已经看到有几个内置函数（pg_description和col_description），但我无法找到如何使用它们的例子，并且使用它们已经证明是非常徒劳的。

所以我想知道以前有没有能够做到这一点，如果有，怎么做？

Answer 1

SELECT c.table_schema,c.table_name,c.column_name,pgd.description
FROM pg_catalog.pg_statio_all_tables as st
  inner join pg_catalog.pg_description pgd on (pgd.objoid=st.relid)
  inner join information_schema.columns c on (pgd.objsubid=c.ordinal_position
    and  c.table_schema=st.schemaname and c.table_name=st.relname);

Answer 2

这一切都是由oid工作，

mat=> SELECT c.oid FROM pg_catalog.pg_class c WHERE c.relname = 'customers';
  oid  
-------
 23208
(1 row)

现在，我有那张桌子的oid，所以我可以问：

mat=> select pg_catalog.obj_description(23208);
  obj_description  
-------------------
 Customers
(1 row)

然后，我可以要求第四栏的描述：

mat=> select pg_catalog.col_description(23208,4);
             col_description             
-----------------------------------------
 Customer codes, CHS, FACTPOST, POWER...
(1 row)

如果您想知道在执行psql或\dt+时\d+ customers运行哪些查询，请使用-E运行。

Answer 3

注意模式，这段代码考虑它们：

SELECT
    cols.column_name,
    (
        SELECT
            pg_catalog.col_description(c.oid, cols.ordinal_position::int)
        FROM
            pg_catalog.pg_class c
        WHERE
            c.oid = (SELECT ('"' || cols.table_name || '"')::regclass::oid)
            AND c.relname = cols.table_name
    ) AS column_comment
FROM
    information_schema.columns cols
WHERE
    cols.table_catalog    = 'your_database'
    AND cols.table_name   = 'your_table'
    AND cols.table_schema = 'your_schema';

参考文献：

• Postgresql Document Table and Column Description Comments on Table and Column

• Determining the OID of a table in Postgres 9.1?

Answer 4

这适用于我使用PostBooks 3.2.2 DB：

select cols.column_name,
(select pg_catalog.obj_description(oid) from pg_catalog.pg_class c where c.relname=cols.table_name) as table_comment
,(select pg_catalog.col_description(oid,cols.ordinal_position::int) from pg_catalog.pg_class c where c.relname=cols.table_name) as column_comment
from information_schema.columns cols
where cols.table_catalog='postbooks' and cols.table_name='apapply'

此致 Sylnsr

Answer 5

如果有人需要它，就在这里。

这里有很多答案，但没有一个像我希望的那么简单。因此，基于之前的答案和当前的postgres 9.4，我创建了这个查询：

SELECT 
    obj_description(format('%s.%s',isc.table_schema,isc.table_name)::regclass::oid, 'pg_class') as table_description,
    pg_catalog.col_description(format('%s.%s',isc.table_schema,isc.table_name)::regclass::oid,isc.ordinal_position) as column_description
FROM
    information_schema.columns isc

它获取表和列描述，没有任何混乱的连接和丑陋的字符串连接。

Answer 6

增强@Nick和@mat建议：使用
SELECT obj_description('schemaName.tableName'::regclass, 'pg_class'); 当你有字符串名称（而不是oid）。

为了避免记住'pg_class'参数，并避免函数调用中的丑陋连接，(tname||'.'||schema)::regclass，obj_description的有用重载：

  CREATE FUNCTION obj_description(
      p_rname text, p_schema text DEFAULT NULL, 
      p_catalname text DEFAULT 'pg_class'
  ) RETURNS text AS $f$
     SELECT obj_description((CASE 
        WHEN strpos($1, '.')>0 OR $2 IS NULL OR $2='' THEN $1
        ELSE $2||'.'||$1
     END)::regclass, $3);
  $f$ LANGUAGE SQL IMMUTABLE;
 -- USAGE: obj_description('mytable') 
 --        SELECT obj_description('s.t'); 
 -- PS: obj_description('s.t', 'otherschema') is a syntax error, 
 --     but not generates exception: returns the same as ('s.t') 

现在很容易使用，因为表名（rname参数）是一个varchar，可以用模式名称的单独字段表示，如在主表和查询中一样。

另请参阅“Getting list of table comments in PostgreSQL”或new pg9.3 Guide

Answer 7

这个答案有点晚了，但它出现在谷歌搜索我做了研究这个问题。我们只需要表描述，但列的方法是相同的。 列描述也在pg_description表中，由objoid引用。

添加此视图：

CREATE OR REPLACE VIEW our_tables AS 
 SELECT c.oid, n.nspname AS schemaname, c.relname AS tablename, d.description,
   pg_get_userbyid(c.relowner) AS tableowner, t.spcname AS "tablespace", 
   c.relhasindex AS hasindexes, c.relhasrules AS hasrules, c.reltriggers > 0 AS hastriggers
   FROM pg_class c
   LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
   LEFT JOIN pg_tablespace t ON t.oid = c.reltablespace
   LEFT JOIN pg_description d ON c.oid = d.objoid
  WHERE c.relkind = 'r'::"char";

ALTER TABLE our_tables OWNER TO postgres;
GRANT SELECT, UPDATE, INSERT, DELETE, REFERENCES, TRIGGER ON TABLE our_tables TO postgres;
GRANT SELECT ON TABLE our_tables TO public;

然后运行：

SELECT tablename, description FROM our_tables WHERE schemaname = 'public'

视图是pg_tables视图的修改版本，它在description列中添加。 您还可以使用视图定义来进行单个查询。

Answer 8

对其中一个其他答案略有改动，这些答案只会为您提供对其有评论的列，这会为您提供所有列是否有评论。

select c.table_schema, st.relname as TableName, c.column_name, 
pgd.description
from pg_catalog.pg_statio_all_tables as st
inner join information_schema.columns c
on c.table_schema = st.schemaname
and c.table_name = st.relname
left join pg_catalog.pg_description pgd
on pgd.objoid=st.relid
and pgd.objsubid=c.ordinal_position
where st.relname = 'YourTableName';

Answer 9

好的，所以我一直在努力学习......

选择col_description（表格ID，列号）......

即：选择col_description（36698,2）;

这很有效，但有没有一种更简单的方法可以将所有的注释放在所有列上并使用表名而不是oid ???

Answer 10

上个月我问a similar question about Postgresql comments。如果你深入研究，你会在我的博客上看到一些Perl代码，它会自动提取评论的过程。

要提取表格的列名，您可以使用以下内容：

select
     a.attname  as "colname"
    ,a.attrelid as "tableoid"
    ,a.attnum   as "columnoid"
from
    pg_catalog.pg_attribute a
    inner join pg_catalog.pg_class c on a.attrelid = c.oid
where
        c.relname = 'mytable' -- better to use a placeholder
    and a.attnum > 0
    and a.attisdropped is false
    and pg_catalog.pg_table_is_visible(c.oid)
order by a.attnum

然后，您可以使用tableoid，columnoid元组来提取每列的注释（请参阅我的问题）。

Answer 11

我刚才在这里找到了。它将为您提供一个特定表上的所有类型的元数据（类型，默认值，非空标志，长度，注释，外键名称，主键名称）。它似乎运作良好。

SELECT pg_tables.tablename, pg_attribute.attname AS field, 
    format_type(pg_attribute.atttypid, NULL) AS "type", 
    pg_attribute.atttypmod AS len,
    (SELECT col_description(pg_attribute.attrelid, 
            pg_attribute.attnum)) AS comment, 
    CASE pg_attribute.attnotnull 
        WHEN false THEN 1  ELSE 0  
    END AS "notnull", 
    pg_constraint.conname AS "key", pc2.conname AS ckey, 
    (SELECT pg_attrdef.adsrc FROM pg_attrdef 
        WHERE pg_attrdef.adrelid = pg_class.oid 
        AND pg_attrdef.adnum = pg_attribute.attnum) AS def 
FROM pg_tables, pg_class 
JOIN pg_attribute ON pg_class.oid = pg_attribute.attrelid 
    AND pg_attribute.attnum > 0 
LEFT JOIN pg_constraint ON pg_constraint.contype = 'p'::"char" 
    AND pg_constraint.conrelid = pg_class.oid AND
    (pg_attribute.attnum = ANY (pg_constraint.conkey)) 
LEFT JOIN pg_constraint AS pc2 ON pc2.contype = 'f'::"char" 
    AND pc2.conrelid = pg_class.oid 
    AND (pg_attribute.attnum = ANY (pc2.conkey)) 
WHERE pg_class.relname = pg_tables.tablename  
--    AND pg_tables.tableowner = "current_user"() 
    AND pg_attribute.atttypid <> 0::oid  
    AND tablename='your_table' 
ORDER BY field ASC

来源：http://golden13.blogspot.de/2012/08/how-to-get-some-information-about_7.html

Answer 12

我访问了这样的表格评论：

select c.relname table_name, pg_catalog.obj_description(c.oid) as comment from pg_catalog.pg_class c where c.relname = 'table_name';

和专栏评论：

SELECT c.column_name, pgd.description FROM pg_catalog.pg_statio_all_tables as st inner join pg_catalog.pg_description pgd on (pgd.objoid=st.relid) inner join information_schema.columns c on (pgd.objsubid=c.ordinal_position and c.table_schema=st.schemaname and c.table_name=st.relname and c.table_name = 'table_name' and c.table_schema = 'public');

Answer 13

如果您只需要在其他数据中为列显示comments，则还可以使用：

\d+ my_table

Answer 14

要显示所有表格的所有列的评论：

SELECT
    cols.table_name,
    cols.column_name, (
    SELECT
        pg_catalog.col_description(c.oid, cols.ordinal_position::int)
    FROM
        pg_catalog.pg_class c
    WHERE
            c.oid = (SELECT ('"' || cols.table_name || '"')::regclass::oid)
      AND c.relname = cols.table_name
) AS column_comment
FROM
    information_schema.columns cols
WHERE
  cols.table_name   IN (SELECT cols.table_name FROM information_schema.columns)
  AND cols.table_catalog = 'your_database_name'
  AND cols.table_schema = 'your_schema_name';

您需要在任何架构/目录/数据库之外执行此查询

此查询基于此问题中的另一个答案，该答案仅显示一个表中的评论