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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