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https://issues.apache.org/jira/browse/DRILL-4081?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Venki Korukanti resolved DRILL-4081.
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Resolution: Fixed
Fix Version/s: 1.4.0
> Handle schema changes in ExternalSort
> -------------------------------------
>
> Key: DRILL-4081
> URL: https://issues.apache.org/jira/browse/DRILL-4081
> Project: Apache Drill
> Issue Type: Improvement
> Reporter: Steven Phillips
> Assignee: Steven Phillips
> Fix For: 1.4.0
>
>
> This improvement will make use of the Union vector to handle schema changes.
> When a new schema appears, the schema will be "merged" with the previous
> schema. The result will be a new schema that uses Union type to store the
> columns where this is a type conflict. All of the batches (including the
> batches that have already arrived) will be coerced into this new schema.
> A new comparison function will be included to handle the comparison of Union
> type. Comparison of union type will work as follows:
> 1. All numeric types can be mutually compared, and will be compared using
> Drill implicit cast rules.
> 2. All other types will not be compared against other types, but only among
> values of the same type.
> 3. There will be an overall precedence of types with regards to ordering.
> This precedence is not yet defined, but will be as part of the work on this
> issue.
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