Return clickhouse array as column

Question

Is it possible with Clickhouse to have result containing a pair of array transformed as columns?

Form this result:

┌─f1──┬f2───────┬f3─────────────┐
│ 'a' │ [1,2,3] │ ['x','y','z'] │
│ 'b' │ [4,5,6] │ ['x','y','z'] │
└─────┴─────────┴───────────────┘

to :

┌─f1──┬x──┬y──┬z──┐
│ 'a' │ 1 │ 2 │ 3 │
│ 'b' │ 4 │ 5 │ 6 │
└─────┴───┴───┴───┘

The idea is to not have to repeat the header values for each line.

In my case, the "header" array f3 unique by queries and join to the f1,f2.

Answer 1

You can do it with help of indexOf function.

SELECT *
FROM test_sof 

┌─f1─┬─f2──────┬─f3────────────┐
│ a  │ [1,2,3] │ ['x','y','z'] │
└────┴─────────┴───────────────┘
┌─f1─┬─f2────────┬─f3────────────────┐
│ c  │ [7,8,9,0] │ ['x','y','z','n'] │
└────┴───────────┴───────────────────┘
┌─f1─┬─f2─────────┬─f3────────────────┐
│ d  │ [7,8,9,11] │ ['x','y','z','n'] │
└────┴────────────┴───────────────────┘
┌─f1─┬─f2──────┬─f3────────────┐
│ b  │ [4,5,6] │ ['x','y','z'] │
└────┴─────────┴───────────────┘

4 rows in set. Elapsed: 0.001 sec.

Then:

SELECT 
    f1, 
    f2[indexOf(f3, 'x')] AS x, 
    f2[indexOf(f3, 'y')] AS y, 
    f2[indexOf(f3, 'z')] AS z, 
    f2[indexOf(f3, 'n')] AS n
FROM test_sof 
ORDER BY 
    f1 ASC, 
    x ASC

┌─f1─┬─x─┬─y─┬─z─┬──n─┐
│ a  │ 1 │ 2 │ 3 │  0 │
│ b  │ 4 │ 5 │ 6 │  0 │
│ c  │ 7 │ 8 │ 9 │  0 │
│ d  │ 7 │ 8 │ 9 │ 11 │
└────┴───┴───┴───┴────┘

4 rows in set. Elapsed: 0.002 sec. 

Keep in mind situation when index from header array will not be present in data array or vise-versa.

UPD: the way how to get data without knowing "headers".

You will get three columns, third one with headers.

SELECT 
    f1, 
    f2[num] AS f2_el, 
    f3[num] AS f3_el
FROM test_sof 
ARRAY JOIN arrayEnumerate(f2) AS num
ORDER BY f1 ASC

┌─f1─┬─f2_el─┬─f3_el─┐
│ a  │     1 │ x     │
│ a  │     2 │ y     │
│ a  │     3 │ z     │
│ b  │     4 │ x     │
│ b  │     5 │ y     │
│ b  │     6 │ z     │
│ c  │     7 │ x     │
│ c  │     8 │ y     │
│ c  │     9 │ z     │
│ c  │     0 │ n     │
│ d  │     7 │ x     │
│ d  │     8 │ y     │
│ d  │     9 │ z     │
│ d  │    11 │ n     │
└────┴───────┴───────┘

14 rows in set. Elapsed: 0.006 sec.