如何将“精简”PostgreSQL行扩展为单独的列？

Question

我有一个返回表的函数。

如果您运行SELECT * FROM some_function(12345)，结果为：

object_id | name
----------------
    12345 | "B"

如果您运行SELECT some_function(12345)，结果为：

some_function
-------------
(12345,"B")

问题是我想要原始表单（以便我可以访问单个列值），但是some_function()的参数来自表中的列。我可以执行SELECT some_function(thing_id) FROM things，但这会返回：

some_function
-------------
(12345,"B")
(12346,"C")
(12347,"D")

而我想要的是：

object_id | name
----------------
    12345 | "B"
    12346 | "C"
    12347 | "D"

那么一个人怎么可能不会＆＃34;或＆＃34;扩展＆＃34;这样一个浓缩的行？

Answer 1

9.3及以上：横向查询

在PostgreSQL 9.3或更新版本中使用隐式横向查询：

SELECT f.* FROM things t, some_function(t.thing_id) f;

首选此配方所有新查询。以上是标准配方。

它也适用于RETURNS TABLE或RETURNS SETOF RECORD的函数以及RETURNS RECORD的out-params的函数。

它的简写：

SELECT f.*
FROM things t
CROSS JOIN LATERAL some_function(t.thing_id) f;

9.3之前：通配符扩展（小心）

之前的版本会导致some_function的多重评估，如果some_function返回一个不，那么不是否正常工作：不使用此：< / p>

SELECT (some_function(thing_id)).* FROM things;

以前的版本，避免使用第二层间接对some_function进行多重评估。只有在你必须支持相当旧的PostgreSQL版本时才使用它。

SELECT (f).*
FROM (
  SELECT some_function(thing_id) f
  FROM things
) sub(f);

演示：

设定：

CREATE FUNCTION some_function(i IN integer, x OUT integer, y OUT text, z OUT text) RETURNS record LANGUAGE plpgsql AS $$
BEGIN
  RAISE NOTICE 'evaluated with %',i;
  x := i;
  y := i::text;
  z := 'dummy';
  RETURN;
END;
$$;

create table things(thing_id integer);
insert into things(thing_id) values (1),(2),(3);

试运行：

demo=>     SELECT f.* FROM things t, some_function(t.thing_id) f;
NOTICE:  evaluated with 1
NOTICE:  evaluated with 2
NOTICE:  evaluated with 3
 x | y |   z   
---+---+-------
 1 | 1 | dummy
 2 | 2 | dummy
 3 | 3 | dummy
(3 rows)

demo=>     SELECT (some_function(thing_id)).* FROM things;
NOTICE:  evaluated with 1
NOTICE:  evaluated with 1
NOTICE:  evaluated with 1
NOTICE:  evaluated with 2
NOTICE:  evaluated with 2
NOTICE:  evaluated with 2
NOTICE:  evaluated with 3
NOTICE:  evaluated with 3
NOTICE:  evaluated with 3
 x | y |   z   
---+---+-------
 1 | 1 | dummy
 2 | 2 | dummy
 3 | 3 | dummy
(3 rows)

demo=>  SELECT (f).*
    FROM (
      SELECT some_function(thing_id) f
      FROM things
    ) sub(f);
NOTICE:  evaluated with 1
NOTICE:  evaluated with 2
NOTICE:  evaluated with 3
 x | y |   z   
---+---+-------
 1 | 1 | dummy
 2 | 2 | dummy
 3 | 3 | dummy
(3 rows)

Answer 2

SELECT * FROM (SELECT some_function(thing_id) FROM things) x;

子选择SELECT some_function(thing_id) FROM things为找到的每条记录返回一行。外部选择＆＃34;解压缩＆＃34;该行分为不同的列。