从 PostgreSQL 数据库中检索评论
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【中文标题】从 PostgreSQL 数据库中检索评论【英文标题】:Retrieving Comments from a PostgreSQL DB 【发布时间】:2010-09-25 11:33:32 【问题描述】: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】:
PostgreSQL 不是很友好,但这是因为每个用户都有你个人的(非标准的)“util library”。在我的库的一个函数(rel_description
)下面,可以帮助你。
【参考方案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);
【讨论】:
我不太明白这段代码是如何工作的,但它可以满足我的需要,所以我不必这样做。 我遇到了一个案例,肯定有表格,结果集的大小为 0。有些事情不太对劲 效果很好,但查询很复杂。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。
按表名过滤并按行数排序: where table_name='parametros_gestora_academica' order by c.ordinal_position ;【参考方案2】:
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】:
"obj_description(object_oid)" 现已弃用,请参阅 postgresql.org/docs/current/static/functions-info.html【参考方案3】: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:
Postgresql Document Table and Column Description Comments on Table and Column
Determining the OID of a table in Postgres 9.1?
【讨论】:
以下行允许表名的更多灵活性:c.oid = (SELECT ('"' || cols.table_name || '"')::regclass::oid) AND
@jcristovao,你能解释得更好吗?
我使用该行以便在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
@MarcioMazzucato:参见postgresql.org/docs/current/datatype-oid.html,regclass
类型将字符串作为输入并为其找到相应的对象 OID。【参考方案4】:
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】:
【参考方案5】: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】:
它可以工作,但是 Postgres 文档中的一个小注释: obj_description 的单参数形式只需要对象 OID。现在不推荐使用它,因为不能保证 OID 在不同的系统目录中是唯一的;因此,可能会返回错误的评论。【参考方案6】: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】:
谢谢,相当于Oracle中的user_col_cmets 这对我来说效果最好,并且能够正确处理混合大小写的表和模式名称。干杯!【参考方案7】: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】:
【参考方案8】: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】:
【参考方案9】: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】:
【参考方案10】: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】:
【参考方案11】: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】:
【参考方案12】: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】:
【参考方案13】: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】:
【参考方案14】: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】:
【参考方案15】: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;
结果:
【讨论】:
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