### What changes were proposed in this pull request?
We have supported generators in SQL aggregate expressions by SPARK-28782.
But, the generator(explode) query with aggregate functions in DataFrame failed as follows;
```
// SPARK-28782: Generator support in aggregate expressions
scala> spark.range(3).toDF("id").createOrReplaceTempView("t")
scala> sql("select explode(array(min(id), max(id))) from t").show()
+---+
|col|
+---+
| 0|
| 2|
+---+
// A failure case handled in this pr
scala> spark.range(3).select(explode(array(min($"id"), max($"id")))).show()
org.apache.spark.sql.AnalysisException:
The query operator `Generate` contains one or more unsupported
expression types Aggregate, Window or Generate.
Invalid expressions: [min(`id`), max(`id`)];;
Project [col#46L]
+- Generate explode(array(min(id#42L), max(id#42L))), false, [col#46L]
+- Range (0, 3, step=1, splits=Some(4))
at org.apache.spark.sql.catalyst.analysis.CheckAnalysis.failAnalysis(CheckAnalysis.scala:49)
at org.apache.spark.sql.catalyst.analysis.CheckAnalysis.failAnalysis$(CheckAnalysis.scala:48)
at org.apache.spark.sql.catalyst.analysis.Analyzer.failAnalysis(Analyzer.scala:129)
```
The root cause is that `ExtractGenerator` wrongly replaces a project w/ aggregate functions
before `GlobalAggregates` replaces it with an aggregate as follows;
```
scala> sql("SET spark.sql.optimizer.planChangeLog.level=warn")
scala> spark.range(3).select(explode(array(min($"id"), max($"id")))).show()
20/03/01 12:51:58 WARN HiveSessionStateBuilder$$anon$1:
=== Applying Rule org.apache.spark.sql.catalyst.analysis.Analyzer$ResolveReferences ===
!'Project [explode(array(min('id), max('id))) AS List()] 'Project [explode(array(min(id#72L), max(id#72L))) AS List()]
+- Range (0, 3, step=1, splits=Some(4)) +- Range (0, 3, step=1, splits=Some(4))
20/03/01 12:51:58 WARN HiveSessionStateBuilder$$anon$1:
=== Applying Rule org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractGenerator ===
!'Project [explode(array(min(id#72L), max(id#72L))) AS List()] Project [col#76L]
!+- Range (0, 3, step=1, splits=Some(4)) +- Generate explode(array(min(id#72L), max(id#72L))), false, [col#76L]
! +- Range (0, 3, step=1, splits=Some(4))
20/03/01 12:51:58 WARN HiveSessionStateBuilder$$anon$1:
=== Result of Batch Resolution ===
!'Project [explode(array(min('id), max('id))) AS List()] Project [col#76L]
!+- Range (0, 3, step=1, splits=Some(4)) +- Generate explode(array(min(id#72L), max(id#72L))), false, [col#76L]
! +- Range (0, 3, step=1, splits=Some(4))
// the analysis failed here...
```
To avoid the case in `ExtractGenerator`, this pr addes a condition to ignore generators having aggregate functions.
A correct sequence of rules is as follows;
```
20/03/01 13:19:06 WARN HiveSessionStateBuilder$$anon$1:
=== Applying Rule org.apache.spark.sql.catalyst.analysis.Analyzer$ResolveReferences ===
!'Project [explode(array(min('id), max('id))) AS List()] 'Project [explode(array(min(id#27L), max(id#27L))) AS List()]
+- Range (0, 3, step=1, splits=Some(4)) +- Range (0, 3, step=1, splits=Some(4))
20/03/01 13:19:06 WARN HiveSessionStateBuilder$$anon$1:
=== Applying Rule org.apache.spark.sql.catalyst.analysis.Analyzer$GlobalAggregates ===
!'Project [explode(array(min(id#27L), max(id#27L))) AS List()] 'Aggregate [explode(array(min(id#27L), max(id#27L))) AS List()]
+- Range (0, 3, step=1, splits=Some(4)) +- Range (0, 3, step=1, splits=Some(4))
20/03/01 13:19:06 WARN HiveSessionStateBuilder$$anon$1:
=== Applying Rule org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractGenerator ===
!'Aggregate [explode(array(min(id#27L), max(id#27L))) AS List()] 'Project [explode(_gen_input_0#31) AS List()]
!+- Range (0, 3, step=1, splits=Some(4)) +- Aggregate [array(min(id#27L), max(id#27L)) AS _gen_input_0#31]
! +- Range (0, 3, step=1, splits=Some(4))
```
### Why are the changes needed?
A bug fix.
### Does this PR introduce any user-facing change?
No.
### How was this patch tested?
Added tests.
Closes#27749 from maropu/ExplodeInAggregate.
Authored-by: Takeshi Yamamuro <yamamuro@apache.org>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>
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