[SPARK-4322][SQL] Enables struct fields as sub expressions of grouping fields

While resolving struct fields, the resulted `GetField` expression is wrapped with an `Alias` to make it a named expression. Assume `a` is a struct instance with a field `b`, then `"a.b"` will be resolved as `Alias(GetField(a, "b"), "b")`. Thus, for this following SQL query:

```sql
SELECT a.b + 1 FROM t GROUP BY a.b + 1
```

the grouping expression is

```scala
Add(GetField(a, "b"), Literal(1, IntegerType))
```

while the aggregation expression is

```scala
Add(Alias(GetField(a, "b"), "b"), Literal(1, IntegerType))
```

This mismatch makes the above SQL query fail during the both analysis and execution phases. This PR fixes this issue by removing the alias when substituting aggregation expressions.

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Author: Cheng Lian <lian@databricks.com>

Closes #3248 from liancheng/spark-4322 and squashes the following commits:

23a46ea [Cheng Lian] Code simplification
dd20a79 [Cheng Lian] Should only trim aliases around `GetField`s
7f46532 [Cheng Lian] Enables struct fields as sub expressions of grouping fields

1 files changed, 11 insertions, 1 deletions

diff --git a/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
index 5dd777f1fb..ce5672c086 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
@@ -551,7 +551,7 @@ class SQLQuerySuite extends QueryTest with BeforeAndAfterAll {
       sql("SELECT * FROM upperCaseData EXCEPT SELECT * FROM upperCaseData"), Nil)
   }
 
- test("INTERSECT") {
+  test("INTERSECT") {
     checkAnswer(
       sql("SELECT * FROM lowerCaseData INTERSECT SELECT * FROM lowerCaseData"),
       (1, "a") ::
@@ -949,4 +949,14 @@ class SQLQuerySuite extends QueryTest with BeforeAndAfterAll {
     checkAnswer(sql("SELECT key FROM testData WHERE value not like '100%' order by key"),
         (1 to 99).map(i => Seq(i)))
   }
+
+  test("SPARK-4322 Grouping field with struct field as sub expression") {
+    jsonRDD(sparkContext.makeRDD("""{"a": {"b": [{"c": 1}]}}""" :: Nil)).registerTempTable("data")
+    checkAnswer(sql("SELECT a.b[0].c FROM data GROUP BY a.b[0].c"), 1)
+    dropTempTable("data")
+
+    jsonRDD(sparkContext.makeRDD("""{"a": {"b": 1}}""" :: Nil)).registerTempTable("data")
+    checkAnswer(sql("SELECT a.b + 1 FROM data GROUP BY a.b + 1"), 2)
+    dropTempTable("data")
+  }
 }