[GitHub] [druid] smic-datalabs-von edited a comment on issue #10548: Plan cannot be built when using virtual column and UNION ALL in SQL query

[GitBox <gi...@apache.org>]

smic-datalabs-von edited a comment 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 unfortunately requires the query to be like the second snippet.
   


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