PostgreSQL:使用其他表的模式和表名吗?


8

考虑一下我所有的模式名称都放在一个表中而我的所有表名称都放在另一个表中的情况。

是否可以执行以下操作(伪代码)?

SELECT value FROM (SELECT schema_name FROM schemas).(SELECT table_name FROM tables)

还是我必须将查询分为三个SELECT?

Answers:


7

杰克已经证明了要走的路。但是,我觉得还有改进的余地。

我将所有内容都放在架构中x以方便测试。测试设置:

DROP SCHEMA x CASCADE;
CREATE SCHEMA x;

-- meta tables for schema and table name    
CREATE TABLE x.schma(schma_id int, schma text);
INSERT INTO  x.schma VALUES (1, 'x');

CREATE TABLE x.tbl(tbl_id int, tbl text);
INSERT INTO  x.tbl VALUES (1, 't1'), (2, 't2');

-- dummy tables to be used in example query:
CREATE TABLE x.t1(id int);
INSERT INTO  x.t1 VALUES (1),(2);

CREATE TABLE x.t2(foo text);
INSERT INTO  x.t2 VALUES ('some text'), ('some more text');

旧功能(原始答案):

CREATE OR REPLACE FUNCTION x.f_dynaquery_old(int, int, _col text, _type anyelement, OUT col anyelement)
  RETURNS SETOF anyelement AS
$func$
BEGIN
   RETURN QUERY EXECUTE '
   SELECT ' || quote_ident(_col) || '
   FROM   ' || (
       (SELECT schma FROM schma WHERE schma_id = $1) || '.' ||
       (SELECT tbl   FROM tbl   WHERE tbl_id   = $2))::regclass;
END
$func$  LANGUAGE plpgsql;

较干净的版本format()(更新于2017年):

CREATE OR REPLACE FUNCTION x.f_dynaquery(_schma_id int, _tbl_id int
                                       , _col text, _type anyelement)
  RETURNS TABLE(col anyelement) AS
$func$
BEGIN
   RETURN QUERY EXECUTE format(
      'SELECT %I FROM %I.%I'
    , _col
    , (SELECT schma FROM schma WHERE schma_id = _schma_id)
    , (SELECT tbl   FROM tbl   WHERE tbl_id   = _tbl_id)
   );
END
$func$  LANGUAGE plpgsql;

COMMENT ON FUNCTION x.f_dynaquery(int, int, text, anyelement)
IS 'Query any column from a dynamically assembled tablename.
$1 .. id of schema
$2 .. id of table
$3 .. name of column
$4 .. type of column (only data type matters, not the value)';

呼叫:

SELECT col FROM x.f_dynaquery(1, 1, 'id', NULL::int);
  col
-----
   1
   2


SELECT col FROM x.f_dynaquery(1, 2, 'foo', NULL::text);
  col
----------------
 some text
 some more text

要点


@JackDouglas:我以您的示例为基础,因此您可能对此示例感兴趣。
Erwin Brandstetter

1
我是偶然发现的-如果我不是发帖人,除非我对帖子发表评论,否则'@'不会出现。以为您想知道:)
杰克说请尝试topanswers.xyz 2011年

@JackDouglas:啊,我不知道这样的评论没有收到您。谢谢(你的)信息!
Erwin Brandstetter

6

您需要动态SQL-也许像这样:

create role stack;
create schema authorization stack;
set role stack;

create or replace function f(p_schema in text, p_table in text)
                           returns setof integer language plpgsql immutable as $$
begin
  return query execute 'select value from '||p_schema||'.'||p_table;
end;$$;

create table t1(value integer);
insert into t1(value) values (1);
insert into t1(value) values (2);

create table t2(value integer);
insert into t2(value) values (1);

create table schemas(schema_name text);
insert into schemas(schema_name) values ('stack');

create table tables(table_name text);
insert into tables(table_name) values ('t1');
insert into tables(table_name) values ('t2');
insert into tables(table_name) values ('t1');
insert into tables(table_name) values ('t2');

select f(schema_name, table_name) from schemas cross join tables;
 f
---
 1
 2
 1
(3 rows)

我假设问题暗示每个表都存在于每个模式中

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