smic-datalabs-von commented on issue #10548:
URL: https://github.com/apache/druid/issues/10548#issuecomment-884010117
I encountered this error as well. I am using Superset to create a Sankey
diagram. My data source for this is a virtual dataset coming from a SQL query
issued on Druid that uses `UNION ALL`. Superset then treats this as a subquery
and issues a GROUP BY.
This is the `UNION ALL` query similar to what I have:
```sql
SELECT
a AS column_1
, b AS column_2
, SUM(metric) AS metric
FROM table
UNION ALL
b AS column_1
, c AS column_2
, SUM(metric) AS metric
FROM table
```
In Superset, this is then placed in a subquery and GROUP BY aggregation is
made:
```sql
SELECT
column_1 AS column_1
, column_2 as column_2
, SUM(metric) AS metric
FROM (
-- Place the UNION ALL query above here...
)
GROUP BY column_1, column_2
```
If the query does not contain any aggregations or GROUP BY, it succeeds. For
example:
```sql
SELECT
column_1 AS column_1
, column_2 as column_2
, metric AS metric -- metric column is not aggregated
FROM (
-- Place the UNION ALL query above here...
)
-- No GROUP BY
```
I could have used the third query, but using the Sankey visual in Superset
requires it to be a query like the second snippet.
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