Gengliang Wang created SPARK-34769:
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Summary: AnsiTypeCoercion: return narrowest convertible type among
TypeCollection
Key: SPARK-34769
URL: https://issues.apache.org/jira/browse/SPARK-34769
Project: Spark
Issue Type: Sub-task
Components: SQL
Affects Versions: 3.2.0
Reporter: Gengliang Wang
Assignee: Gengliang Wang
Currently, when implicit casting a data type to a `TypeCollection`, Spark
returns the first convertible data type among `TypeCollection`.
In ANSI mode, we can make the behavior more reasonable by returning the
narrowest convertible data type in `TypeCollection`.
In details, we first try to find the all the expected types we can implicitly
cast:
1. if there is no convertible data types, return None;
2. if there is only one convertible data type, cast input as it;
3. otherwise if there are multiple convertible data types, find the narrowest
common data
type among them. If there is no such narrowest common data type, return
None.
Note that if the narrowest common type is Float type and the convertible types
contains Double ype, simply return Double type as the narrowest common type to
avoid potential
precision loss on converting the Integral type as Float type.
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