[jira] [Created] (SPARK-16947) Improve type coercion of inline tables

["Herman van Hovell (JIRA)" <ji...@apache.org>]

Herman van Hovell created SPARK-16947:
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             Summary: Improve type coercion of inline tables
                 Key: SPARK-16947
                 URL: https://issues.apache.org/jira/browse/SPARK-16947
             Project: Spark
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 2.1.0
            Reporter: Herman van Hovell
            Assignee: Herman van Hovell


Inline tables were added in to Spark SQL in 2.0, e.g.: {{select * from values (1, 'A'), (2, 'B') as tbl(a, b)}}

This is currently implemented using a {{LocalRelation}} and this relation is created during parsing. This has several weaknesses: you can only use simple expressions in such a plan, and type coercion is based on the first row in the relation, and all subsequent values are cast in to this type. The latter violates the principle of least surprise.

I would like to rewrite this into a union of projects; each of these projects would contain a single table row. We apply better type coercion rules to a union, and we should be able to rewrite this into a local relation during optimization. 



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