How to combine two queries where one of them results in an array and the second is the element place in the array? - sql

Question

I have the following two queries:
Query #1
(SELECT ARRAY (SELECT (journeys.id)
FROM JOURNEYS
JOIN RESPONSES ON scenarios[1] = responses.id) AS arry);
This one returns an array.
Query #2:
SELECT (journeys_index.j_index)
FROM journeys_index
WHERE environment = 'env1'
AND for_channel = 'ch1'
AND first_name = 'name1';
This second query returns the element index in the former array.
How do I combine the two to get only the element value?

Answer 1

I recreated a simpler example with a table containing an array column (the result of your first query)
create table my_array_test (id int, tst_array varchar[]);
insert into my_array_test values (1,'{cat, mouse, frog}');
insert into my_array_test values (2,'{horse, crocodile, rabbit}');
And another table containing the element position for each row I want to extract.
create table my_array_pos_test (id int, pos int);
insert into my_array_pos_test values (1,1);
insert into my_array_pos_test values (2,3);
e.g. from the row in my_array_test with id=1 I want to extract the 1st item (pos=1) and from the row in my_array_test with id=2 I want to extract the 3rd item (pos=3)
defaultdb=> select * from my_array_pos_test;
id | pos
----+-----
1 | 1
2 | 3
(2 rows)
Now the resulting statement is
select *,
tst_array[my_array_pos_test.pos]
from
my_array_test join
my_array_pos_test on my_array_test.id = my_array_pos_test.id
with the expected result
id | tst_array | id | pos | tst_array
----+--------------------------+----+-----+-----------
1 | {cat,mouse,frog} | 1 | 1 | cat
2 | {horse,crocodile,rabbit} | 2 | 3 | rabbit
(2 rows)
Now, in your case I would probably do something similar to the below, assuming your 1st select statement returns one row only.
with array_sel as
(SELECT ARRAY (SELECT (journeys.id)
FROM JOURNEYS
JOIN RESPONSES ON scenarios[1] = responses.id) AS arry)
SELECT arry[journeys_index.j_index]
FROM journeys_index cross join array_sel
WHERE environment = 'env1'
AND for_channel = 'ch1'
AND first_name = 'name1';
I can't validate fully the above sql statement since we can't replicate your tables, but should give you a hint on where to start from