我有一个使用表继承的PostgreSQL 8.3数据库。我想通过查询获取所有继承自基础表的表名以及其模式名称列表。是否有方法可以使用PGSQL来实现此功能?
我有一个使用表继承的PostgreSQL 8.3数据库。我想通过查询获取所有继承自基础表的表名以及其模式名称列表。是否有方法可以使用PGSQL来实现此功能?
由于你使用的是如此老的 PostgreSQL 版本,你可能需要使用 PL/PgSQL 函数来处理继承深度大于 1 的情况。在现代 PostgreSQL 中(甚至是 8.4),你可以使用递归公共表达式 (WITH RECURSIVE
)。
pg_catalog.pg_inherits
表是关键。假设有:
create table pp( ); -- The parent we'll search for
CREATE TABLE notpp(); -- Another root for multiple inheritance
create table cc( ) inherits (pp); -- a 1st level child of pp
create table dd( ) inherits (cc,notpp); -- a 2nd level child of pp that also inherits aa
create table notshown( ) inherits (notpp); -- Table that inherits only notpp
create table ccdd () inherits (cc,dd) -- Inheritance is a graph not a tree; join node
正确的结果将会找到 cc
, dd
, 和 ccdd
, 但不会找到 notpp
或 notshown
。
一个单层次查询是:
SELECT pg_namespace.nspname, pg_class.relname
FROM pg_catalog.pg_inherits
INNER JOIN pg_catalog.pg_class ON (pg_inherits.inhrelid = pg_class.oid)
INNER JOIN pg_catalog.pg_namespace ON (pg_class.relnamespace = pg_namespace.oid)
WHERE inhparent = 'pp'::regclass;
...但这只能找到cc
。
对于多级继承(例如tableC
继承自tableB
,tableB
又继承自tableA
),您需要通过递归CTE或在PL/PgSQL中使用循环来扩展该功能,将上一个循环的子项作为下一个循环的父项。
更新:以下是一个与8.3兼容的版本,应该递归地找到从给定父项直接或间接继承的所有表。如果使用了多重继承,则应该找到在树的任何点上具有目标表作为其父项之一的任何表。
CREATE OR REPLACE FUNCTION find_children(oid) RETURNS SETOF oid as $$
SELECT i.inhrelid FROM pg_catalog.pg_inherits i WHERE i.inhparent = $1
UNION
SELECT find_children(i.inhrelid) FROM pg_catalog.pg_inherits i WHERE i.inhparent = $1;
$$ LANGUAGE 'sql' STABLE;
CREATE OR REPLACE FUNCTION find_children_of(parentoid IN regclass, schemaname OUT name, tablename OUT name) RETURNS SETOF record AS $$
SELECT pg_namespace.nspname, pg_class.relname
FROM find_children($1) inh(inhrelid)
INNER JOIN pg_catalog.pg_class ON (inh.inhrelid = pg_class.oid)
INNER JOIN pg_catalog.pg_namespace ON (pg_class.relnamespace = pg_namespace.oid);
$$ LANGUAGE 'sql' STABLE;
使用方法:
regress=# SELECT * FROM find_children_of('pp'::regclass);
schemaname | tablename
------------+-----------
public | cc
public | dd
public | ccdd
(3 rows)
这是递归的CTE版本,如果你更新了Pg,它将会起作用,但不会在你当前的版本上起作用。在我看来,这样更加简洁。
WITH RECURSIVE inh AS (
SELECT i.inhrelid FROM pg_catalog.pg_inherits i WHERE inhparent = 'pp'::regclass
UNION
SELECT i.inhrelid FROM inh INNER JOIN pg_catalog.pg_inherits i ON (inh.inhrelid = i.inhparent)
)
SELECT pg_namespace.nspname, pg_class.relname
FROM inh
INNER JOIN pg_catalog.pg_class ON (inh.inhrelid = pg_class.oid)
INNER JOIN pg_catalog.pg_namespace ON (pg_class.relnamespace = pg_namespace.oid);
public.base_table_name
表的所有子表:select bt.relname as table_name, bns.nspname as table_schema
from pg_class ct
join pg_namespace cns on ct.relnamespace = cns.oid and cns.nspname = 'public'
join pg_inherits i on i.inhparent = ct.oid and ct.relname = 'base_table_name'
join pg_class bt on i.inhrelid = bt.oid
join pg_namespace bns on bt.relnamespace = bns.oid
虽然我不是100%确定,但它应该可以与8.3兼容。
对于那些使用支持RECURSIVE
的PostgreSQL版本的人,这里有一个函数,可以找到指定基表的派生表。
CREATE OR REPLACE FUNCTION tables_derived_from(base_namespace name, base_table name)
RETURNS TABLE (table_schema name, table_name name, oid oid)
AS $BODY$
WITH RECURSIVE inherited_id AS
(
SELECT i.inhrelid AS oid
FROM pg_inherits i
JOIN pg_class base_t ON i.inhparent = base_t.oid
JOIN pg_namespace base_ns ON base_t.relnamespace = base_ns.oid
WHERE base_ns.nspname = base_namespace AND base_t.relname = base_table
UNION
SELECT i.inhrelid AS oid
FROM pg_inherits i
JOIN inherited_id b ON i.inhparent = b.oid
)
SELECT child_ns.nspname as table_schema, child_t.relname as table_name, child_t.oid
FROM inherited_id i
JOIN pg_class child_t ON i.oid = child_t.oid
JOIN pg_namespace child_ns ON child_t.relnamespace = child_ns.oid
ORDER BY 1, 2, 3;
$BODY$ LANGUAGE sql STABLE;
需要注意的是,一个表可以继承多个表,而且上述解决方案都没有充分展示这一点;它们只是遍历单个父级树。请考虑以下情况:
CREATE TABLE a();
CREATE TABLE b();
CREATE TABLE ab_() INHERITS (a,b);
CREATE TABLE ba_() INHERITS (b,a);
CREATE TABLE ab__() INHERITS (ab_);
CREATE TABLE ba__() INHERITS (ba_);
CREATE TABLE ab_ba_() INHERITS (ab_, ba_);
CREATE TABLE ba_ab_() INHERITS (ba_, ab_);
WITH RECURSIVE inh AS (
SELECT i.inhparent::regclass, i.inhrelid::regclass, i.inhseqno FROM pg_catalog.pg_inherits i WHERE inhparent = 'a'::regclass
UNION
SELECT i.inhparent::regclass, i.inhrelid::regclass, i.inhseqno FROM inh INNER JOIN pg_catalog.pg_inherits i ON (inh.inhrelid = i.inhparent)
) SELECT * FROM inh;
inhparent | inhrelid | inhseqno
-----------+----------+----------
a | ab_ | 1
a | ba_ | 2
ab_ | ab__ | 1
ba_ | ba__ | 1
ab_ | ab_ba_ | 1
ba_ | ab_ba_ | 2
ba_ | ba_ab_ | 1
ab_ | ba_ab_ | 2
(8 rows)
inhrelid path
ab_ {"{a,b}"}
ba_ {"{b,a}"}
ab_ba_ {"{a,b}","{b,a}"}
inhrelid parents
ab_ {a,b}
ba_ {b,a}
ab_ba_ {ab_,ba_}