Add a test for accessing nested filter in filter in aggregation

Signed-off-by: Yuanchun Shen <yuanchu@amazon.com>

Author: yuancu

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalciteExplainIT.java

@@ -2427,4 +2427,14 @@ public void testFilterOnMultipleCascadedNestedFields() throws IOException {
                     + " < 6 and author.books.title = 'The Shining'",
                 TEST_INDEX_CASCADED_NESTED)));
   }
+
+  @Test
+  public void testAggFilterOnNestedFields() throws IOException {
+    assertYamlEqualsIgnoreId(
+        loadExpectedPlan("agg_filter_nested.yaml"),
+        explainQueryYaml(
+            StringUtils.format(
+                "source=%s | stats count(eval(author.name < 'K')) as george_and_jk",
+                TEST_INDEX_CASCADED_NESTED)));
+  }
 }

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalciteWhereCommandIT.java

@@ -19,6 +19,7 @@
 import java.util.Map;
 import org.json.JSONObject;
 import org.junit.Test;
+import org.opensearch.sql.common.utils.StringUtils;
 import org.opensearch.sql.ppl.WhereCommandIT;
 
 public class CalciteWhereCommandIT extends WhereCommandIT {
@@ -140,4 +141,15 @@ public void testScriptFilterOnDifferentNestedHierarchyShouldThrow() throws IOExc
         "Accessing multiple nested fields under different hierarchies in script is not supported:"
             + " [author.books.reviews, author.books]");
   }
+
+  @Test
+  public void testAggFilterOnNestedFields() throws IOException {
+    JSONObject result =
+        executeQuery(
+            StringUtils.format(
+                "source=%s | stats count(eval(author.name < 'K')) as george_and_jk",
+                TEST_INDEX_CASCADED_NESTED));
+    verifySchema(result, schema("george_and_jk", "bigint"));
+    verifyDataRows(result, rows(2));
+  }
 }

integ-test/src/test/resources/expectedOutput/calcite/agg_filter_nested.yaml

@@ -0,0 +1,9 @@
+calcite:
+  logical: |
+    LogicalSystemLimit(fetch=[10000], type=[QUERY_SIZE_LIMIT])
+      LogicalAggregate(group=[{}], george_and_jk=[COUNT($0)])
+        LogicalProject($f1=[CASE(<($7, 'K'), 1, null:NULL)])
+          CalciteLogicalIndexScan(table=[[OpenSearch, opensearch-sql_test_index_cascaded_nested]])
+  physical: |
+    EnumerableLimit(fetch=[10000])
+      CalciteEnumerableIndexScan(table=[[OpenSearch, opensearch-sql_test_index_cascaded_nested]], PushDownContext=[[AGGREGATION->rel#:LogicalAggregate.NONE.[](input=RelSubset#,group={},george_and_jk=COUNT() FILTER $0)], OpenSearchRequestBuilder(sourceBuilder={"from":0,"size":0,"timeout":"1m","aggregations":{"george_and_jk":{"filter":{"nested":{"query":{"range":{"author.name":{"from":null,"to":"K","include_lower":true,"include_upper":false,"boost":1.0}}},"path":"author","ignore_unmapped":false,"score_mode":"none","boost":1.0}},"aggregations":{"george_and_jk":{"value_count":{"field":"_index"}}}}}}, requestedTotalSize=2147483647, pageSize=null, startFrom=0)])

integ-test/src/test/resources/expectedOutput/calcite_no_pushdown/agg_filter_nested.yaml

@@ -0,0 +1,11 @@
+calcite:
+  logical: |
+    LogicalSystemLimit(fetch=[10000], type=[QUERY_SIZE_LIMIT])
+      LogicalAggregate(group=[{}], george_and_jk=[COUNT($0)])
+        LogicalProject($f1=[CASE(<($7, 'K'), 1, null:NULL)])
+          CalciteLogicalIndexScan(table=[[OpenSearch, opensearch-sql_test_index_cascaded_nested]])
+  physical: |
+    EnumerableLimit(fetch=[10000])
+      EnumerableAggregate(group=[{}], george_and_jk=[COUNT() FILTER $0])
+        EnumerableCalc(expr#0..13=[{inputs}], expr#14=['K'], expr#15=[<($t7, $t14)], expr#16=[IS TRUE($t15)], $f1=[$t16])
+          CalciteEnumerableIndexScan(table=[[OpenSearch, opensearch-sql_test_index_cascaded_nested]])