Hello crdb friends,

I tested the following statements on crdb and received error messages:

```
root@:26257/defaultdb> create table test4 (id int not null primary key, data jsonb not null);
CREATE TABLE
Time: 34.379874ms
root@:26257/defaultdb> insert into test4 values (1, '{"a": {"b": {"c": [1,2,3]}}}'),(2, '{"x": {"y": {"z": [1,3,5]}}}'),(3, '{"a": {"b": {"c": [1,4,5]}}}');
INSERT 3
Time: 21.268096ms
root@:26257/defaultdb> select * from test4;
id | data
+----+--------------------------------+
1 | {"a": {"b": {"c": [1, 2, 3]}}}
2 | {"x": {"y": {"z": [1, 3, 5]}}}
3 | {"a": {"b": {"c": [1, 4, 5]}}}
(3 rows)
root@:26257/defaultdb> select data->'a'->'b'->'c'->0 firstel from test4;
firstel
+---------+
1
NULL
1
(3 rows)
root@:26257/defaultdb> select data->'a'->'b'->'c'->0 firstel, count(*) freq from test4 group by data->'a'->'b'->'c'->0 order by 1;
pq: can't order by column type jsonb
root@:26257/defaultdb> select data->'a'->'b'->'c'->0 firstel, count(*) freq from test4 group by data->'a'->'b'->'c'->0;
pq: unable to encode table key: *tree.DJSON
```

But they executed as expected in PG.

Is this simply a yet supported feature or is it more of a bug?

Thanks.