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https://issues.apache.org/jira/browse/SPARK-33300?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17224937#comment-17224937
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Aoyuan Liao commented on SPARK-33300:
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I would like to work on this.
> Rule SimplifyCasts will not work for nested columns
> ---------------------------------------------------
>
> Key: SPARK-33300
> URL: https://issues.apache.org/jira/browse/SPARK-33300
> Project: Spark
> Issue Type: Bug
> Components: Optimizer, SQL
> Affects Versions: 3.0.0
> Reporter: chendihao
> Priority: Minor
>
> We use SparkSQL and Catalyst to optimize the Spark job. We have read the
> source code and test the rule of SimplifyCasts which will work for simple SQL
> without nested cast.
> The SQL "select cast(string_date as string) from t1" will be optimized.
> {code:java}
> == Analyzed Logical Plan ==
> string_date: string
> Project [cast(string_date#12 as string) AS string_date#24]
> +- SubqueryAlias t1
> +- LogicalRDD [name#8, c1#9, c2#10, c5#11L, string_date#12,
> string_timestamp#13, timestamp_field#14, bool_field#15], false
> == Optimized Logical Plan ==
> Project [string_date#12]
> +- LogicalRDD [name#8, c1#9, c2#10, c5#11L, string_date#12,
> string_timestamp#13, timestamp_field#14, bool_field#15], false
> {code}
> However, it fail to optimize with the nested cast like this "select
> cast(cast(string_date as string) as string) from t1".
> {code:java}
> == Analyzed Logical Plan ==
> CAST(CAST(string_date AS STRING) AS STRING): string
> Project [cast(cast(string_date#12 as string) as string) AS
> CAST(CAST(string_date AS STRING) AS STRING)#24]
> +- SubqueryAlias t1
> +- LogicalRDD [name#8, c1#9, c2#10, c5#11L, string_date#12,
> string_timestamp#13, timestamp_field#14, bool_field#15], false
> == Optimized Logical Plan ==
> Project [string_date#12 AS CAST(CAST(string_date AS STRING) AS STRING)#24]
> +- LogicalRDD [name#8, c1#9, c2#10, c5#11L, string_date#12,
> string_timestamp#13, timestamp_field#14, bool_field#15], false
> {code}
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