viirya commented on a change in pull request #25215: [SPARK-28445][SQL][Python]
Fix error when PythonUDF is used in both group by and aggregate expression
URL: https://github.com/apache/spark/pull/25215#discussion_r308231137
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/python/ExtractPythonUDFs.scala
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@@ -81,6 +81,64 @@ object ExtractPythonUDFFromAggregate extends
Rule[LogicalPlan] {
}
}
+/**
+ * Extracts PythonUDFs in logical aggregate, which are used in grouping keys,
evaluate them
+ * before aggregate.
+ * This must be executed after `ExtractPythonUDFFromAggregate` rule and before
`ExtractPythonUDFs`.
+ */
+object ExtractGroupingPythonUDFFromAggregate extends Rule[LogicalPlan] {
Review comment:
ExtractPythonUDFFromAggregate pulls out Python UDFs which have aggregate
expression or grouping key as input, like udf(sum(c)), and Python UDFs which
have no input. Those UDFs pulled out are evaluated after aggregate.
This rule, ExtractGroupingPythonUDFFromAggregate, pulls out Python UDFs
which are used in grouping keys, like `SELECT count(*) FROM table GROUP BY
udf(id)`. This kind of Python UDF is evaluated before aggregate.
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