From 040fb3e0a6a13a69b3288ad2bfc13d1b672a4142 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Mon, 24 Nov 2025 09:14:49 +0000
Subject: [PATCH] Grouping key field type can only be overwritten when the
 ExprCoreType are different (#4850)

Signed-off-by: Lantao Jin <ltjin@amazon.com>
(cherry picked from commit 1c27a6db9b570b34e585cc42987a71f2f53bb8f3)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
---
 .../rest-api-spec/test/issues/4845.yml        | 49 +++++++++++++++++++
 .../value/OpenSearchExprValueFactory.java     | 13 +++--
 2 files changed, 59 insertions(+), 3 deletions(-)
 create mode 100644 integ-test/src/yamlRestTest/resources/rest-api-spec/test/issues/4845.yml

diff --git a/integ-test/src/yamlRestTest/resources/rest-api-spec/test/issues/4845.yml b/integ-test/src/yamlRestTest/resources/rest-api-spec/test/issues/4845.yml
new file mode 100644
index 00000000000..ba1ccd1256b
--- /dev/null
+++ b/integ-test/src/yamlRestTest/resources/rest-api-spec/test/issues/4845.yml
@@ -0,0 +1,49 @@
+setup:
+  - do:
+      query.settings:
+        body:
+          transient:
+            plugins.calcite.enabled: true
+  - do:
+      indices.create:
+        index: test
+        body:
+          mappings:
+            properties:
+              "EventDate":
+                type: date
+                format: yyyy-MM-dd HH:mm:ss||strict_date_optional_time||epoch_millis
+  - do:
+      bulk:
+        index: test
+        refresh: true
+        body:
+          - '{"index": {"_id": "1"}}'
+          - '{"EventDate": "2013-07-15 10:47:34"}'
+
+---
+teardown:
+  - do:
+      query.settings:
+        body:
+          transient:
+            plugins.calcite.enabled : false
+
+---
+"handle custom format field with pushdown":
+  - skip:
+      features:
+        - headers
+        - allowed_warnings
+  - do:
+      allowed_warnings:
+        - 'Loading the fielddata on the _id field is deprecated and will be removed in future versions. If you require sorting or aggregating on this field you should also include the id in the body of your documents, and map this field as a keyword field that has [doc_values] enabled'
+      headers:
+        Content-Type: 'application/json'
+      ppl:
+        body:
+          query: source=test | stats count() by EventDate
+
+  - match: { total: 1 }
+  - match: {"schema": [{"name": "count()", "type": "bigint"},{"name": "EventDate", "type": "timestamp"}]}
+  - match: {"datarows": [[1, "2013-07-15 10:47:34"]]}
diff --git a/opensearch/src/main/java/org/opensearch/sql/opensearch/data/value/OpenSearchExprValueFactory.java b/opensearch/src/main/java/org/opensearch/sql/opensearch/data/value/OpenSearchExprValueFactory.java
index af5c2732778..f75c7961f52 100644
--- a/opensearch/src/main/java/org/opensearch/sql/opensearch/data/value/OpenSearchExprValueFactory.java
+++ b/opensearch/src/main/java/org/opensearch/sql/opensearch/data/value/OpenSearchExprValueFactory.java
@@ -81,13 +81,20 @@ public class OpenSearchExprValueFactory {
   private final boolean fieldTypeTolerance;
 
   /**
-   * Extend existing mapping by new data without overwrite. Called from aggregation only {@see
-   * AggregationQueryBuilder#buildTypeMapping}.
+   * Extend existing mapping by new data. Overwrite only when the ExprCoreType of them are
+   * different. Called from aggregation only {@see AggregationQueryBuilder#buildTypeMapping}.
    *
    * @param typeMapping A data type mapping produced by aggregation.
    */
   public void extendTypeMapping(Map<String, OpenSearchDataType> typeMapping) {
-    this.typeMapping.putAll(typeMapping);
+    typeMapping.forEach(
+        (groupKey, extendedType) -> {
+          OpenSearchDataType existedType = this.typeMapping.get(groupKey);
+          if (existedType == null
+              || !existedType.getExprCoreType().equals(extendedType.getExprCoreType())) {
+            this.typeMapping.put(groupKey, extendedType);
+          }
+        });
   }
 
   @Getter @Setter private OpenSearchAggregationResponseParser parser;