Fix case insensitive resolution of GetField.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala

@@ -21,6 +21,7 @@ import org.apache.spark.sql.catalyst.errors.TreeNodeException
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.plans.logical._
 import org.apache.spark.sql.catalyst.rules._
+import org.apache.spark.sql.catalyst.types.StructType
 
 /**
  * A trivial [[Analyzer]] with an [[EmptyCatalog]] and [[EmptyFunctionRegistry]]. Used for testing
@@ -187,6 +188,15 @@ class Analyzer(catalog: Catalog,
             val result = q.resolveChildren(name, resolver).getOrElse(u)
             logDebug(s"Resolving $u to $result")
             result
+
+          // Resolve field names using the resolver.
+          case f @ GetField(child, fieldName) if !f.resolved && child.resolved =>
+            child.dataType match {
+              case StructType(fields) =>
+                val resolvedFieldName = fields.map(_.name).find(resolver(_, fieldName))
+                resolvedFieldName.map(n => f.copy(fieldName = n)).getOrElse(f)
+              case _ => f
+            }
         }
     }
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypes.scala

@@ -92,7 +92,13 @@ case class GetField(child: Expression, fieldName: String) extends UnaryExpressio
 
   lazy val ordinal = structType.fields.indexOf(field)
 
-  override lazy val resolved = childrenResolved && child.dataType.isInstanceOf[StructType]
+  override lazy val resolved = childrenResolved && fieldResolved
+
+  /** Returns true only if the fieldName is found in the child struct. */
+  private def fieldResolved = child.dataType match {
+    case StructType(fields) => fields.map(_.name).contains(fieldName)
+    case _ => false
+  }
 
   override def eval(input: Row): Any = {
     val baseValue = child.eval(input).asInstanceOf[Row]

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveResolutionSuite.scala

@@ -27,6 +27,17 @@ case class Data(a: Int, B: Int, n: Nested, nestedArray: Seq[Nested])
  * A set of test cases expressed in Hive QL that are not covered by the tests included in the hive distribution.
  */
 class HiveResolutionSuite extends HiveComparisonTest {
+
+  case class NestedData(a: Seq[NestedData2], B: NestedData2)
+  case class NestedData2(a: NestedData3, B: NestedData3)
+  case class NestedData3(a: Int, B: Int)
+
+  test("SPARK-3698: case insensitive test for nested data") {
+    sparkContext.makeRDD(Seq.empty[NestedData]).registerTempTable("nested")
+    // This should be successfully analyzed
+    sql("SELECT a[0].A.A from nested").queryExecution.analyzed
+  }
+
   createQueryTest("table.attr",
     "SELECT src.key FROM src ORDER BY key LIMIT 1")