Sorting user-defined array with strings gives wrong order, even when file content is fully available on disk

I am querying ElasticSearch and sorting the documents locally in Bash with jq, as sorting in ES is too slow for me.

The original purpose is to create a CSV file.

But I find the sorting does not work properly, it seems sort step does nothing.

As I am launching cURL requests, I thought the wrong order is due to content is chunked so I save some results into a local test.json file and tried again, but it still does not work.

test.json:

{"took": 680,"timed_out": false,"_shards": {"total": 1,"successful": 1,"skipped": 0,"failed": 0    },"hits": {"max_score": 1.0,"hits": [            {"_index": "my-index","_type": "_doc","_id": "111111113584925","_score": 1.0,"fields": {"field2": ["FOO"                    ],"field1": ["111111113584925"                    ]                }            },            {"_index": "my-index","_type": "_doc","_id": "111111121254059","_score": 1.0,"fields": {"field2": ["FOO"                    ],"field1": ["111111121254059"                    ]                }            }        ]    }}

(There are many more records - edited for brevity.)

Command that I use:

jq '.hits.hits[].fields | [.field1[0] +"," + .field2[0]] | sort | .[0]' -r test.json

The result:

111111113584925,FOO111111121254059,FOO111111116879444,FOO

etc.

Why?

Should I rely on jq sorting? Am I using it correctly? I mean I want to do string comparison by alphabetical order, and field1 all have unique values, so it will never be a tie and start to compare values of field2(it also could have various values but I only want to sort by field1)

Should I use Bash sort -k 1 instead? Which is faster when it comes to 100K rows?