Ngone51 opened a new pull request #28572:
URL: https://github.com/apache/spark/pull/28572
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### What changes were proposed in this pull request?
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Eliminate the `UpCast` if it's child data type is already decimal type.
### Why are the changes needed?
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While deserializing internal `Decimal` value to external
`BigDecimal`(Java/Scala) value, Spark should also respect `Decimal`'s precision
and scale, otherwise it will cause precision lost and look weird in some cases,
e.g.:
```
sql("select cast(11111111111111111111111111111111111111 as decimal(38, 0))
as d")
.write.mode("overwrite")
.parquet(f.getAbsolutePath)
// can fail
spark.read.parquet(f.getAbsolutePath).as[BigDecimal]
```
```
[info] org.apache.spark.sql.AnalysisException: Cannot up cast `d` from
decimal(38,0) to decimal(38,18).
[info] The type path of the target object is:
[info] - root class: "scala.math.BigDecimal"
[info] You can either add an explicit cast to the input data or choose a
higher precision type of the field in the target object;
[info] at
org.apache.spark.sql.catalyst.analysis.Analyzer$ResolveUpCast$.org$apache$spark$sql$catalyst$analysis$Analyzer$ResolveUpCast$$fail(Analyzer.scala:3060)
[info] at
org.apache.spark.sql.catalyst.analysis.Analyzer$ResolveUpCast$$anonfun$apply$33$$anonfun$applyOrElse$174.applyOrElse(Analyzer.scala:3087)
[info] at
org.apache.spark.sql.catalyst.analysis.Analyzer$ResolveUpCast$$anonfun$apply$33$$anonfun$applyOrElse$174.applyOrElse(Analyzer.scala:3071)
[info] at
org.apache.spark.sql.catalyst.trees.TreeNode.$anonfun$transformDown$1(TreeNode.scala:309)
[info] at
org.apache.spark.sql.catalyst.trees.CurrentOrigin$.withOrigin(TreeNode.scala:72)
[info] at
org.apache.spark.sql.catalyst.trees.TreeNode.transformDown(TreeNode.scala:309)
[info] at
org.apache.spark.sql.catalyst.trees.TreeNode.$anonfun$transformDown$3(TreeNode.scala:314)
```
### Does this PR introduce _any_ user-facing change?
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Yes, for cases(cause precision lost) mentioned above will fail before this
change but run successfully after this change.
### How was this patch tested?
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Added tests.
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