vogievetsky opened a new issue #8947: Unnecessary cartesian explosion if multi-value column is reused in expression URL: https://github.com/apache/incubator-druid/issues/8947 ### Affected Version Druid 0.16, 0.15 ### Description With this dataset (as `fs`): ```json {"time":"2019-08-14T00:00:00.000Z","srcGroups":["x","y","z"],"dstGroups":["a","b","c","d"]} {"time":"2019-08-14T00:00:00.000Z","srcGroups":["x","y","z"],"dstGroups":["a","c","d"]} {"time":"2019-08-14T00:00:00.000Z","srcGroups":["x","y","z"],"dstGroups":["a","g"]} ``` Doing this query: ```sql SELECT CASE "dstGroups" WHEN 'b' THEN 'b' WHEN 'g' THEN 'g' ELSE 'Other' END AS "dst", COUNT(*) AS "Count" FROM "fs" GROUP BY 1 ORDER BY "Count" DESC ``` Yields an unexpected cartesian explosion:  This is due to this expression in the underlying plan: `"case_searched((\"dstGroups\" == 'b'),'b',(\"dstGroups\" == 'g'),'g','Other')"` Which triggers a cartesian product on the same column `dstGroups` which it should not do.
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