jq: repeat value from one object when iterating through array elements in another object

Input:

{
  "level1": {
    "id": "a"
  },
  "level2": [
    {
      "id": "1"
    },
    {
      "id": "2"
    }
  ]
}
{
  "level1": {
    "id": "b"
  },
  "level2": [
    {
      "id": "3"
    },
    {
      "id": "4"
    }
  ]
}

Expected output:

a  1 
a  2 
b  3 
b  4 

What I basically want to accomplish is:

jq -r '[ .level1.id, (.level2[] |.id ) ]|@tsv'

where .level1.id repeats for every object in the .level2 array but I don’t seem to be able to think about the problem the right way

>Solution :

Using .level2[] within another array constructor (the outer […]) just collects all items iterated over into that constructed array. Separate them to iterate outside another array, make both parts create (sub)arrays themselves, then add them together:

[.level1.id] + (.level2[] | [.id]) | @tsv

Demo

Alternatively, use variables which you can reference from inside the array constructor:

.level2[] as {$id} | [.level1.id, $id] | @tsv

Demo

Output:

a   1
a   2
b   3
b   4