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https://issues.apache.org/jira/browse/DRILL-6824?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Arina Ielchiieva updated DRILL-6824:
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Labels: ready-to-commit (was: )
> Drill Query on MapRDB JSON table failing on schema SchemaChangeException, the
> only distinct Values are NULL and Text
> --------------------------------------------------------------------------------------------------------------------
>
> Key: DRILL-6824
> URL: https://issues.apache.org/jira/browse/DRILL-6824
> Project: Apache Drill
> Issue Type: Bug
> Affects Versions: 1.14.0
> Reporter: Gautam Parai
> Assignee: Gautam Parai
> Priority: Major
> Labels: ready-to-commit
> Fix For: 1.15.0
>
> Original Estimate: 24h
> Remaining Estimate: 24h
>
> Drill Query on MapR DB JSON Table or it View fails with a
> SchemaChangeException. The only distinct values is NULL and some Text.
> The issue is that when Drill sees a NULL or does not see any values for a
> column in the first batch it assumes the type as NULLABLE INT. Subsequently,
> when the data shows up and it is different from NULLABLE INT there is a
> schema change. Operators e.g. aggregators etc. cannot handle such a Schema
> Change and throw a SchemaChangeException.
>
> One of the short-term solution implemented in this fix: Add a CAST expression
> which will cast null values to the target type. Hence, we would never see a
> SchemaChange due to NULLs. However, the MapRDB Reader code was written
> differently than other reader and was hitting a SchemaChangeException. The
> code was changed to make it similar to other scans i.e. emit a new batch
> whenever a schema change is encountered.
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