I don't see the value with this suggestion. It isn't going to make things
much better since the user will be totally stunned when the structure
doesn't come through as an array.
A bigger issue is the fact that elements of maps aren't marked correctly as
missing. That means that if I have these two records:
"a":{"first": 1, "second": 2}, b:3
"a"={"second":20, "third":30}, b:5
it is nearly impossible for me to determine whether "first" is missing from
the second value of "a". This makes Drill impossible to use for lots of
variant structure work. The values that Drill provides will have all fields
marked as present.
(at least, this was true at one time).
On Sun, Nov 19, 2017 at 4:33 AM, Paul Rogers <[email protected]> wrote:
> Hi Arina,
>
> The proposal is to represent 2D arrays as a string (using the original,
> unparsed JSON.) That is, given this input:
>
> {a: “fred”, b: [[10, 20, 30], [11, 21, 31]]}
>
> The parsed columns are:
>
> a, b
> “fred”, "[[10, 20, 30], [11, 21, 31]]”
>
> Notice that column b is just a string. It is a string of JSON, yes, but
> still just a string.
>
> So, the question about kvgen/flatten does not apply here since we are not
> creating a Drill array.
>
> There is a very interesting discussion to be had about how Drill
> does/should handle “non-relational” JSON structures. But, here, the
> suggestions is just for one very simple special case.
>
> Thanks,
>
> - Paul
>
> > On Nov 18, 2017, at 7:15 AM, Arina Yelchiyeva <
> [email protected]> wrote:
> >
> > In general sounds good.
> > If user will apply kvgen / flatten over such 2-D array columns read as
> > string, he will be able to normalize data in the format he wants? Right?
> Or
> > we need to come up with new function?
> >
> > Kind regards
> > Arina
> >
> > On Fri, Nov 17, 2017 at 10:39 PM, Paul Rogers <[email protected]> wrote:
> >
> >> Hi All,
> >>
> >> I’d like to propose a minor enhancement to the JSON reader to better
> >> handle non-relational JSON structures. (See DRILL-5974 [1].)
> >>
> >> As background, Drill handles simple tuples:
> >>
> >> {a: 10, b: “fred”}
> >>
> >> Drill also handles arrays:
> >>
> >> {name: “fred”, hobbies: [“bowling”, “golf”]}
> >>
> >> Drill even handles arrays of tuples:
> >>
> >> {name: “fred”, orders: [
> >> {id: 1001, amount: 12.34},
> >> {id: 1002, amount: 56.78}]}
> >>
> >> The above are termed "relational" because there is a straightforward
> >> mapping to/from tables into the above JSON structures.
> >>
> >> Things get interesting with non-relational types, such as 2-D arrays:
> >>
> >> {id: 4, shape: “square”, points: [[0, 0], [0, 5], [5, 0], [5, 5]]}
> >>
> >> Drill has two solutions:
> >>
> >> * Turn on the experimental list and union support.
> >> * Enable all-text mode to read all fields as JSON text.
> >>
> >> Here, I’d like to propose a middle ground:
> >>
> >> * Read fields with relational types into vectors.
> >> * Read non-relational fields using text mode.
> >>
> >> Thus, the first three examples would all result in the JSON data parsed
> >> into Drill vectors. But, the fourth, non-relational example would
> produce a
> >> row that looks like this:
> >>
> >> id, shape, points
> >> 4, “shape”, “[[0, 0], [0, 5], [5, 0], [5, 5]]”
> >>
> >> Although Drill can’t parse the 2-D array, Drill will pass the array
> along
> >> to the client, which can use its favorite JSON parser to parse the array
> >> and do something useful (like draw the square in this case.)
> >>
> >> In particular, the proposal:
> >>
> >> * Apply this change only to the revised “batch size aware” JSON reader.
> >> * Use the above parsing model by default.
> >> * Use the experimental list-and-union support if the existing
> >> `exec.enable_union_type` system/session option is set.
> >>
> >> Existing queries should “just work.” In fact, now JSON with
> non-relational
> >> types will work “out-of-the-box” without all-text mode or the
> experimental
> >> types.
> >>
> >> Thoughts?
> >>
> >> - Paul
> >>
> >> [1] https://issues.apache.org/jira/browse/DRILL-5974
> >>
> >>
> >>
>
>
