Searching element in jsonb_array_elements(2D array) - sql

Question

I have a table with 2 column R(id int,dat jsonb). The b column jsonb consist of a 2D array [][]. For example :
id| dat
1 | {"name":"a","numbers":[[1,2],[3,4],[5,6],[1,3]]}
2 | {"age":5,"numbers":[[1,1]]}
3 | {"numbers":[[5,6],[6,7]]}
I'm trying to find all the ids that contain a specific number in one of those sub arrays. I used 2 solutions and I want to understand why the first one isn't working :
1)
select * from R
where exists (
select from jsonb_array_elements(R.dat->'numbers')->>0 first,jsonb_array_elements(range.data->'numbers')->>1 second where first::decimal= 1 and second::decimal= 1
);
ERROR: syntax error at or near "->>"
LINE 3: ...t from jsonb_array_elements(R.dat->'numbers')->>0 first,j...
SELECT *
FROM R
WHERE EXISTS (
SELECT FROM jsonb_array_elements(R.dat-> 'numbers') subarray
WHERE (subarray->>0)::decimal = 1 and (subarray->>1)::decimal = 1
);
In addition, I saw that gin index doesn't handle this operator so basically does any index will help here ?

Answer 1

Your first query raises an error because you can use only table experssions (not value expressions) in the FROM clause.
You can make the second query a bit simpler:
select *
from r
where exists (
select from jsonb_array_elements(dat->'numbers') subarray
where subarray = '[1,1]'
);
or using the function in a lateral join:
select r.*
from r
cross join jsonb_array_elements(dat->'numbers')
where value = '[1,1]';
There is no index that could support these queries because of the use of jsonb_array_elements().
You may be tempted to use the containment operator #> in the way like this:
select *
from r
where dat->'numbers' #> '[[1,1]]'::jsonb
id | dat
----+------------------------------------------------------------
1 | {"name": "a", "numbers": [[1, 2], [3, 4], [5, 6], [1, 3]]}
2 | {"age": 5, "numbers": [[1, 1]]}
(2 rows)
Unfortunately, as you can see, it does not work as you could expect. The use of the operator on arrays is a bit tricky, as it works in the way: array1 #> array2 is true if for each element j of array2, there is an i in array1 such that i #> j. Hence, per the documentation:
the order of array elements is not significant when doing a containment match, and duplicate array elements are effectively considered only once.