vogievetsky opened a new issue, #16456:
URL: https://github.com/apache/druid/issues/16456
The SQL data loader in the web console uses a VALUES query to make a sample
dataset for easy previewing. I know the description might make this sounds like
a crazy corner case but in actuality this is a very common thing to stumble
upon as in a sample of data (20 rows or so) with many column you are very
likely to get a column that is all NULL.
### Affected Version
All recent Druid versions that I tested including the latest build on master
as of this writing and 30.0.0 RC.
### Description
Here is a very simple (self contained) query that fails:
```sql
SELECT
CAST("c1" AS VARCHAR) AS "channel",
CAST("c2" AS VARCHAR) AS "cityName",
PARSE_JSON("c3") AS "j"
FROM (
VALUES
('ca', NULL, '{}'),
('de', NULL, '{"a":"1"}'),
('de', null, '{"a":"2"}')
) AS "t" ("c1", "c2", "c3")
```
<img width="475" alt="image"
src="https://github.com/apache/druid/assets/177816/88821942-672a-418e-8b77-3318dd9bb734";>
All that is logged in the broker is:
```
2024-05-15T18:43:43,102 WARN [sql[8f567aa7-38c4-4d27-89dc-60189e66f5c9]]
org.apache.druid.sql.http.SqlResource - Exception while processing
sqlQueryId[8f567aa7-38c4-4d27-89dc-60189e66f5c9]
(org.apache.druid.error.DruidException: Unhandled Query Planning Failure, see
broker logs for details)
```
Which is not helpful
Curiously if one of the NULLs is changed to, say a `''` it works:
<img width="442" alt="image"
src="https://github.com/apache/druid/assets/177816/0c4570e3-f70f-43ab-96bf-299f25b92967";>
Also if we remove the `PARSE_JSON` it also works:
<img width="469" alt="image"
src="https://github.com/apache/druid/assets/177816/10019293-7c62-4e34-9bc7-e4abc4f67cee";>
From playing around with this it appears that there is some additional
processing step that applying a function like `PARSE_JSON` adds that can not
handle a NULL typed column that is being cast.
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