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https://issues.apache.org/jira/browse/SPARK-34396?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17280485#comment-17280485
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Apache Spark commented on SPARK-34396:
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User 'ulysses-you' has created a pull request for this issue:
https://github.com/apache/spark/pull/31509
> Add a new build-in function delegate
> ------------------------------------
>
> Key: SPARK-34396
> URL: https://issues.apache.org/jira/browse/SPARK-34396
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.2.0
> Reporter: ulysses you
> Priority: Minor
>
> Delegate is just like a big box that can include some other expressions. It
> will execute all of children and return the last child result as its result.
>
> The origin idea is from debug. Debug SQL is hard since SQL is always quite
> long and complex. This new function can help debug with inject some help
> functions, e.g., `println, sleep, raise_error`.
>
> Two usage examples:
> {code:java}
> -- raw sql
> INSERT INTO TABLE t1
> SELECT coalesce(c1, c2) as c FROM t2
>
> -- print the column data
> INSERT INTO TABLE t1
> SELECT delegate(
> java_method('scala.Console', 'println', concat('c1: ', c1, ', c2: ', c2)),
> coalesce(c1, c2)
> ) as c FROM t2{code}
>
> {code:java}
> -- raw sql
> SELECT if(spark_partition_id() = 1, c1, raise_error('test error')) FROM t2
>
> -- add a sleep time before throw error
> SELECT if(spark_partition_id() = 1, c1, delegate(
> java_method('java.lang.Thread', 'sleep', 3000l),
> raise_error('test error')
> )) FROM t2{code}
>
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