How do I split a row into multiple columns in Presto?

Question

I have a table like below with columns A (string) and B ROW(int):

A   B
a   [1,2,3]
b   [0,0,5]
c   [3,1,4]

And I would like to split the second column (which contains a ROW type) into multiple columns this way:

A   B1 B2 B3
a   1  2  3
b   0  0  5
c   3  1  4

I believe this can be done with a SQL statement, but unnest will create new rows (which I don't want) and split_part does not work with the ROW type. How can I achieve this?

Answer 1

Assuming column B is a ROW type, you can use the .* ROW operator in SELECT statements .

This syntax exists in Trino ( formerly PrestoSQL ) but not PrestoDB, so it depends on which version you're using for this to work. I'd recommend moving to Trino anyways if you haven't already.

Copy/Paste:

WITH t(a, b) AS (
  VALUES
    ('a', ROW(1,2,3)),
    ('b', ROW(0,0,5)),
    ('c', ROW(3,1,4))
  )
SELECT 
  a as A,
  t.b.* AS (B1, B2, B3)
FROM t;

Execution:

trino> WITH t(a, b) AS (
    ->   VALUES
    ->     ('a', ROW(1,2,3)),
    ->     ('b', ROW(0,0,5)),
    ->     ('c', ROW(3,1,4))
    ->   )
    -> SELECT
    ->   a as A,
    ->   t.b.* AS (B1, B2, B3)
    -> FROM t;
 A | B1 | B2 | B3
---+----+----+----
 a |  1 |  2 |  3
 b |  0 |  0 |  5
 c |  3 |  1 |  4
(3 rows)

Answer 2

This is an equivalent answer to the chosen solution, with a slightly different syntax:

SELECT
A,
B[1] AS B1,
B[2] AS B2,
B[3] AS B3
FROM table;