sql: SELECT DISTINCT jsoncol->foo is broken

[benesch]

Realistic reproduction:

> create table t (ext json);
> insert into t values ('{"foo": "bar"}');
> select distinct ext->'foo' from t;
pq: unable to encode table key: *tree.DJSON

Minimal reproduction:

> select distinct '{}'::json;
pq: unable to encode table key: *tree.DJSON

@justinj suggests that this is because we can't currently key-encode JSON values. As a workaround:

> select distinct ext->>'foo' from t;
+-------------+
| ext->>'foo' |
+-------------+
| bar         |
+-------------+
(2 rows)

[benesch]

/cc @nstewart

[awoods187]

Do we have a plan to address this in 2.1 bug fixing period @jordanlewis ?

[jordanlewis]

Unfortunately this isn't fixable in 2.1 - it's too much work. We could potentially put a better error message for it, but I'm not sure it's worth the effort.

[sploiselle]

@justinj Can I get a quick blurb describing this known limitation w/r/t the impact to user experience? Ideally, we need it by Friday 10/26 for the 2.1 Known Limitations page. Posting it on this issue and/or pinging me would be great.

[RaduBerinde]

Similar case that hits the same error: SELECT DISTINCT json_array_elements('[10, 200, 200, 300, 400]');

[knz]

I have added telemetry links inside CockroachDB to the underlying/overarching issue #35706.

[jordanlewis]

Closing as duplicate of #35706.