從記錄類型的單列中分離/提取值，將用戶定義的函數應用於多行CTE

Question

使用PostgreSQL 9.2，我定義了一個函數，它接受一個參數並返回一個多列表。我想將該函數應用於CTE行中的多個參數。我得到的結果是一列元組，而不是我想要的多列。即：

sandbox=# CREATE FUNCTION myfunc(arg int) RETURNS table(col1 int, col2 int) AS 
sandbox-# 'SELECT arg+1, arg+2' 
sandbox-# LANGUAGE SQL; 
CREATE FUNCTION 
sandbox=# select * from myfunc(1); 
col1 | col2 
------+------ 
    2 | 3 
(1 row) 

sandbox=# WITH rows AS (
sandbox(# SELECT 1 AS arg UNION SELECT 2 AS arg 
sandbox(#) 
sandbox-# SELECT * FROM (SELECT myfunc(arg) FROM rows) x; 
myfunc 
-------- 
(2,3) 
(3,4) 
(2 rows) 

鑑於CTE，下面的兩個SELECT條款相同的評估，以對方爲表record類型的單個列：

SELECT myfunc(arg) FROM rows; 
SELECT * FROM (select myfunc(arg) FROM rows) x; 

而且下面三個都失敗（CTE未示出）：

SELECT myfunc(arg).col1 FROM rows; 
ERROR: syntax error at or near "." 
LINE 4: SELECT myfunc(arg).col1 FROM rows; 
         ^

SELECT col1 FROM (select myfunc(arg) FROM rows) x; 
ERROR: column "col1" does not exist 
LINE 4: SELECT col1 FROM (select myfunc(arg) FROM rows) x; 
      ^

SELECT col1 FROM (SELECT * FROM (select myfunc(arg) FROM rows) x) y; 
ERROR: column "col1" does not exist 
LINE 4: SELECT col1 FROM (SELECT * FROM (select myfunc(arg) FROM row... 
      ^

如何獲取包含單列元組中的值的多列表？

Answer 1

在myfunc周圍加上括號很重要。

select (myfunc(arg)).* from rows;