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https://issues.apache.org/jira/browse/SPARK-28348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16882758#comment-16882758
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Yuming Wang commented on SPARK-28348:
-------------------------------------
Sorry. I mean could we avoid set scale number to 6 and then cast it to 18 for
this case?
For example:
{code:sql}
CAST((decimal(p1, s1) * decimal(p2, s2)) as decimal(p3, s3))
{code}
How about just set
[resultType|https://github.com/apache/spark/blob/3139d642fac0e6ae6b9edd1b4c2912c3a69f71e5/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/DecimalPrecision.scala#L103]
to {{decimal(p3, s3)}} because finally we need to cast to {{decimal(p3, s3)}}?
> Avoid cast twice for decimal type
> ---------------------------------
>
> Key: SPARK-28348
> URL: https://issues.apache.org/jira/browse/SPARK-28348
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.3.3
> Reporter: Yuming Wang
> Priority: Major
>
> Spark 2.1:
> {code:scala}
> scala> sql("select cast(cast(-34338492.215397047 as decimal(38, 10)) *
> cast(-34338492.215397047 as decimal(38, 10)) as decimal(38,
> 18))").show(false);
> +-------------------------------------------------------------------------------------------------------------------+
> |CAST((CAST(-34338492.215397047 AS DECIMAL(38,10)) * CAST(-34338492.215397047
> AS DECIMAL(38,10))) AS DECIMAL(38,18))|
> +-------------------------------------------------------------------------------------------------------------------+
> |1179132047626883.596862135856320209
> |
> +-------------------------------------------------------------------------------------------------------------------+
> {code}
> Spark 2.3:
> {code:scala}
> scala> sql("select cast(cast(-34338492.215397047 as decimal(38, 10)) *
> cast(-34338492.215397047 as decimal(38, 10)) as decimal(38,
> 18))").show(false);
> +-------------------------------------------------------------------------------------------------------------------+
> |CAST((CAST(-34338492.215397047 AS DECIMAL(38,10)) * CAST(-34338492.215397047
> AS DECIMAL(38,10))) AS DECIMAL(38,18))|
> +-------------------------------------------------------------------------------------------------------------------+
> |1179132047626883.596862000000000000
> |
> +-------------------------------------------------------------------------------------------------------------------+
> {code}
> I think we do not need to cast result to {{decimal(38, 6)}} and then cast
> result to {{decimal(38, 18)}} for this case.
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