From a10ba49cc8e4741a512b3b9dfbb7d5decbbd2b54 Mon Sep 17 00:00:00 2001
From: Navaneeth Sujith <navaneethsujith09@gmail.com>
Date: Sun, 14 Jun 2026 11:19:28 -0700
Subject: [PATCH] [CH] Support skewness aggregate function

---
 .../scala/org/apache/gluten/utils/CHExpressionUtil.scala   | 1 -
 .../execution/GlutenClickhouseCountDistinctSuite.scala     | 5 ++---
 .../SimpleStatisticsFunctions.cpp                          | 7 +++++++
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/backends-clickhouse/src/main/scala/org/apache/gluten/utils/CHExpressionUtil.scala b/backends-clickhouse/src/main/scala/org/apache/gluten/utils/CHExpressionUtil.scala
index 3bbb4a467f6..e5bee2dc202 100644
--- a/backends-clickhouse/src/main/scala/org/apache/gluten/utils/CHExpressionUtil.scala
+++ b/backends-clickhouse/src/main/scala/org/apache/gluten/utils/CHExpressionUtil.scala
@@ -192,7 +192,6 @@ object CHExpressionUtil {
     URL_DECODE -> DefaultValidator(),
     URL_ENCODE -> DefaultValidator(),
     FORMAT_STRING -> FormatStringValidator(),
-    SKEWNESS -> DefaultValidator(),
     MAKE_YM_INTERVAL -> DefaultValidator(),
     MAP_ZIP_WITH -> DefaultValidator(),
     KURTOSIS -> DefaultValidator(),
diff --git a/backends-clickhouse/src/test/scala/org/apache/gluten/execution/GlutenClickhouseCountDistinctSuite.scala b/backends-clickhouse/src/test/scala/org/apache/gluten/execution/GlutenClickhouseCountDistinctSuite.scala
index 22a82a9439d..2aa0979dacb 100644
--- a/backends-clickhouse/src/test/scala/org/apache/gluten/execution/GlutenClickhouseCountDistinctSuite.scala
+++ b/backends-clickhouse/src/test/scala/org/apache/gluten/execution/GlutenClickhouseCountDistinctSuite.scala
@@ -103,9 +103,8 @@ class GlutenClickhouseCountDistinctSuite extends GlutenClickHouseWholeStageTrans
     // skewness agg is not supported, will cause fallback
     val sql = "select count(distinct(a,b)) , skewness(b) from " +
       "values (0, null,1), (0,null,1), (1, 1,1), (2, 2, 1) ,(2,2,2),(3,3,3) as data(a,b,c)"
-    assertThrows[UnsupportedOperationException] {
-      spark.sql(sql).show
-    }
+    compareResultsAgainstVanillaSpark(sql, true, { _ => })
+
   }
 
   test("check count distinct with expr fallback") {
diff --git a/cpp-ch/local-engine/Parser/aggregate_function_parser/SimpleStatisticsFunctions.cpp b/cpp-ch/local-engine/Parser/aggregate_function_parser/SimpleStatisticsFunctions.cpp
index bda181e0fad..93ed056cbf9 100644
--- a/cpp-ch/local-engine/Parser/aggregate_function_parser/SimpleStatisticsFunctions.cpp
+++ b/cpp-ch/local-engine/Parser/aggregate_function_parser/SimpleStatisticsFunctions.cpp
@@ -63,7 +63,14 @@ class AggregateFunctionParserStddev final : public AggregateFunctionParser
         return func_node;
     }
 };
+// for skewness
+struct SkewnessNameStruct
+{
+    static constexpr auto spark_name = "skewness";
+    static constexpr auto ch_name = "skewSamp";
+};
 
+static const AggregateFunctionParserRegister<AggregateFunctionParserStddev<SkewnessNameStruct>> registerer_skewness;
 static const AggregateFunctionParserRegister<AggregateFunctionParserStddev<StddevNameStruct>> registerer_stddev;
 static const AggregateFunctionParserRegister<AggregateFunctionParserStddev<StddevSampNameStruct>> registerer_stddev_samp;
 }