Details
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Improvement
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Status: Resolved
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Major
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Resolution: Fixed
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Description
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.