我正在 Postgres 数据库上运行一个项目，需要检索数据库中列上的 cmets 以用作表标题等。我已经看到有几个内置函数（pg_description 和 col_description），但我无法找到有关如何使用它们的示例，并且使用它们被证明是徒劳的。
所以我想知道之前是否有人能够做到这一点，如果可以，怎么做？
【问题讨论】：
rel_description）下面，可以帮助你。
标签： postgresql metadata
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);
【讨论】：
pg_statio_all_tables 是重视图，因此不要将其用于检索列描述。很好的解决方案是“T.Z.”的回答。
这一切都由oid工作，
mat=> SELECT c.oid FROM pg_catalog.pg_class c WHERE c.relname = 'customers';
oid
-------
23208
(1 row)
现在，我有那个表的 oid，所以我可以问：
mat=> select pg_catalog.obj_description(23208);
obj_description
-------------------
Customers
(1 row)
那么，我可以询问第四列的描述：
mat=> select pg_catalog.col_description(23208,4);
col_description
-----------------------------------------
Customer codes, CHS, FACTPOST, POWER...
(1 row)
如果您想知道 psql 在您执行 \dt+ 或 \d+ customers 时运行哪些查询，只需使用 -E 运行即可。
【讨论】：
注意架构，这段代码会考虑它们：
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';
参考资料：
【讨论】：
c.oid = (SELECT ('"' || cols.table_name || '"')::regclass::oid) AND
WHERE 子句中只指定一次table_name。但是，cols.table_name 的简单解决方案以 WeirdCaps 之类的表名失败
regclass 类型将字符串作为输入并为其找到相应的对象 OID。
只要有人需要，就在这里。
这里有很多答案，但没有一个像我希望的那样简单。因此，基于以前的答案和当前的 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，没有任何令人困惑的连接和丑陋的字符串连接。
【讨论】：
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'
问候， 合成器
【讨论】：
对其他答案之一稍作更改，它只会为您提供包含 cmets 的列，这将为您提供所有列，无论它们是否有评论。
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';
【讨论】：
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（不是 oid）时。
为了避免记住 'pg_class' 参数，并避免在函数调用时出现丑陋的连接，如 (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 schema name 的分隔字段来表示，如主表和查询。
另见“Getting list of table comments in PostgreSQL”或new pg9.3 Guide
【讨论】：
这个答案有点晚了，但它出现在我为研究这个问题所做的谷歌搜索中。我们只需要表格描述，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'该视图是 pg_tables 视图的修改版本，它添加在描述列中。 您还可以随意使用视图定义以使其成为单个查询。
【讨论】：
我这样访问表 cmets：
select c.relname table_name, pg_catalog.obj_description(c.oid) as comment from pg_catalog.pg_class c where c.relname = 'table_name';
因此列 cmets：
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');
【讨论】：
如果您只需要在其他数据中为您的列显示comments，您也可以使用：
\d+ my_table
【讨论】：
我刚刚在这里找到了这个。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
【讨论】：
好的，所以我解决了这个问题......
选择 col_description(表 id, 列号)...
即：选择 col_description(36698,2);
这行得通，但是有没有更简单的方法可以做到这一点，也许将所有的 cmets 放在所有列上，并使用表名而不是 oid ？？？
【讨论】：
我上个月问过a similar question about Postgresql comments。如果你仔细研究，你会在我的博客上看到一些 Perl 代码，它可以自动提取评论。
要提取表的列名，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）。
【讨论】：
显示所有表中所有列的 cmets：
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，该答案仅显示来自一个表的 cmets
【讨论】：
扩展@amxy 提供的响应；我发现添加模式过滤器在某些环境中会有所帮助。我发现@amxy 的解决方案在我通过模式过滤器添加之前不起作用
SELECT
pg_tables.schemaname,
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.schemaname IN ('op', 'im', 'cs','usr','li')
-- AND pg_tables.tableowner = "current_user"()
AND pg_attribute.atttypid <> 0::oid
---AND TABLENAME='your_table'
ORDER BY pg_tables.schemaname,
pg_tables.TABLENAME ASC;
【讨论】：