postgres jsonb return specific paths of json object

Question

Consider the following jsonb object:

{
  "track": {
    "segments": [
      {
        "location":   [ 47.763, 13.4034 ],
        "startTime": "2018-10-14 10:05:14",
        "HR": 73
      },
      {
        "location":   [ 47.706, 13.2635 ],
        "startTime": "2018-10-14 10:39:21",
        "HR": 135
      }
    ]
  }
}

I would like to query the object, to return only the following jsonb object, given the folloiwng paths:

• track.segments.hr

{
  "track": {
    "segments": [
      {
        "HR": 73
      },
      {
        "HR": 135
      }
    ]
  }
}

How can i formulate the query, to retrieve this kind of data from the json, and still return the json object, with only the specified paths?

Answer 1

You almost certainly can't.

JSON doesn't [yet] have the equivalent of XML's XSLTransform, which could do what you describe, but [still] only after retrieving the entire blob of XML to work with.

Databases are really good at finding little bits of stuff and putting them together; they're far less good and taking large blobs of stuff and pulling them apart.

I assume what you're showing is a simplification but what you've shown could be done easily with ordinary, relational tables.