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.

如果运行SELECT * FROM some_function(12345)结果是:

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

如果运行SELECT some_function(12345)结果是:

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),但让参数some_function()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")

而我想要的回报是:

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

那么如何"不必要"或"扩展"这样一个浓缩的行呢？

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;

对所有新查询都喜欢这个公式.以上是标准配方.

它也可以正常使用函数,RETURNS TABLE或者RETURNS SETOF RECORD使用out-params 函数RETURNS RECORD.

它是以下的简写:

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)

在此之前的版本中,会导致多种评价some_function,也没有如果工作some_function回报一组,请不要使用此:

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

以前的版本,避免了some_function使用第二层间接的多重评估.只有在必须支持相当旧的PostgreSQL版本时才使用它.

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

演示:

建立:

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);

测试运行:

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)