Postgres 用户定义函数：SQL 中的自连接

Question

我有以下 SQL 在 psql 中工作得很好：

SELECT
   parent.relname, child.relname       AS child
FROM pg_inherits
    JOIN pg_class parent            ON pg_inherits.inhparent = parent.oid
    JOIN pg_class child             ON pg_inherits.inhrelid   = child.oid
    JOIN pg_namespace nmsp_parent   ON nmsp_parent.oid  = parent.relnamespace
    JOIN pg_namespace nmsp_child    ON nmsp_child.oid   = child.relnamespace
WHERE parent.relname='table_name';

问题是当我把它放在创建函数块中时：

CREATE OR REPLACE FUNCTION my_function(tablename text)
RETURNS SETOF RECORD AS
$$


  SELECT
   parent.relname, child.relname       AS child
FROM pg_inherits
    JOIN pg_class parent            ON pg_inherits.inhparent = parent.oid
    JOIN pg_class child             ON pg_inherits.inhrelid   = child.oid
    JOIN pg_namespace nmsp_parent   ON nmsp_parent.oid  = parent.relnamespace
    JOIN pg_namespace nmsp_child    ON nmsp_child.oid   = child.relnamespace
WHERE parent.relname= tablename;



$$ LANGUAGE plpgsql;

我收到一个错误：

ERROR:  schema "parent" does not exist
LINE 10:     parent.relname

,

当我尝试 "public.parent.relname" 时，我得到的错误是：

ERROR:  cross-database references are not implemented: 

    public.parent.relname
    LINE 10:     public.parent.relname

如何正确处理这种情况，我的语法有什么问题？

Answer 1

我在您提供的示例中发现了几个错误。我以你的例子为例，有几件事跳出来了：

Return类型未声明（可以是记录，table，自定义类型，...）
未声明语言名称 (plpgsql, sql, c,...)
...

看看 documentation，你可以找到更多关于如何在 PostgreSQL 中创建函数的信息，还有很多例子（google，Whosebug，博客帖子）。

基于您的示例（还取决于 return 类型、语言名称）对我有用的工作示例：

CREATE OR REPLACE FUNCTION my_function()
RETURNS SETOF RECORD AS 
$$ 
SELECT
    parent.relname, child.relname       AS child
FROM pg_inherits
    JOIN pg_class parent            ON pg_inherits.inhparent = parent.oid
    JOIN pg_class child             ON pg_inherits.inhrelid   = child.oid
    JOIN pg_namespace nmsp_parent   ON nmsp_parent.oid  = parent.relnamespace
    JOIN pg_namespace nmsp_child    ON nmsp_child.oid   = child.relnamespace
WHERE parent.relname='table_name';
$$ LANGUAGE sql;

Answer 2

这对我有用：

CREATE OR REPLACE FUNCTION my_function (tablename text)
RETURNS TEXT AS
$$
DECLARE
  ret text := '';

BEGIN

SELECT
    parent.relname, child.relname

FROM pg_inherits
    JOIN pg_class parent            ON pg_inherits.inhparent = parent.oid
    JOIN pg_class child             ON pg_inherits.inhrelid   = child.oid
    JOIN pg_namespace nmsp_parent   ON nmsp_parent.oid  = parent.relnamespace
    JOIN pg_namespace nmsp_child    ON nmsp_child.oid   = child.relnamespace
WHERE parent.relname= tablename;



RETURN ret;


END;


$$ LANGUAGE plpgsql;

因为语言必须 "plpgsql" BEGIN/END 需要块

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