Question

I have a function in PostgreSQL (PLPGSQL) that returns an array containing two elements. When I run a select statement calling the function, I get a column containing the array (as expected):

{1, 2}

What I really would like to do is extract these elements to be their own columns:

[ 1 | 2 ]

I have found that I can do:

SELECT (MyFunction())[1], (MyFunction())[2]

But that calls the function twice, therefore doubling the run time (this function is a very time-consuming function). Is there a better way to handle this?

Here is an almost perfect replica of what I have:

SELECT table1.a, table1.b, table1.c, (MyFunction(table1.a, table1.b, table1.c))[1],
(MyFunction(table1.a, table1.b, table1.c))[2]
FROM table1
INNER JOIN table2 using(b)
WHERE ... GROUP BY table1.a, table1.b, table1.c;

Again, this produces the two columns from the array, but my function is called twice, which doubles my run time.

Answer 1

can you use a subselect?

postgres=# select ar[1], ar[2] from (select string_to_array('a b c', ' ') ar) as sq;
 ar | ar 
----+----
 a  | b
(1 row)

This still requires you explicitly extract each column (like you already do). If there are more elements in the array than extracted, they will be lost, and if there are fewer, then the missing columns will just be NULL.

EDIT: I think I would wrap the whole thing in a subselect; the inner subselect generates the desired rows, with the outer select projecting the inner query into the desired columns:

SELECT subquery1.a, subquery1.b, subquery1.c, 
    myfunction_result[1], myfunction_result[2] 
FROM ( SELECT table1.a, table1.b, table1.c,
              MyFunction(table1.a, table1.b, table1.c) as myfunction_result
       FROM table1 INNER JOIN table2 using(b) 
       WHERE ... GROUP BY table1.a, table1.b, table1.c
) AS subquery1;

The inner and outer selects will properly correlate the table1 references.