[GitHub] [spark] gengliangwang opened a new pull request #24849: [SPARK-28018][SQL] Allow upcasting decimal to double/float

[GitBox <gi...@apache.org>]

gengliangwang opened a new pull request #24849: [SPARK-28018][SQL] Allow upcasting decimal to double/float
URL: https://github.com/apache/spark/pull/24849
 
 
   ## What changes were proposed in this pull request?
   
   Currently, Spark only allows upcasting DecimalType to IntegralType or DecimalType.
   
   This PR proposes: if the target DecimalType is tighter than DoubleType or FloatType, we can upcast it as well.
   The upcasting matters because it blocks https://github.com/apache/spark/pull/24806. E.g, if there is a table "t" with only one column of double type, 
   ```
   INSERT INTO TABLE t SELECT 10.0
   ```
   The data type of value 10.0 is DecimalType(3, 1). In the current code, Spark can't upcast the decimal to the column of double type.
   
   
   ## How was this patch tested?
   
   Unit test 
   

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