Do not optimize GROUP BY functions that shadow their arguments

src/Interpreters/FunctionMaskingArgumentCheckVisitor.h

@@ -0,0 +1,43 @@
+#pragma once
+
+
+#include <DataTypes/Serializations/ISerialization.h>
+#include <Interpreters/InDepthNodeVisitor.h>
+#include <Parsers/ASTFunction.h>
+#include <Parsers/ASTIdentifier.h>
+
+namespace DB
+{
+
+/// Checks from bottom to top if a function's alias shadows the name
+/// of one of it's arguments
+class FunctionMaskingArgumentCheckMatcher
+{
+public:
+    struct Data
+    {
+        const String& alias;
+        bool is_rejected = false;
+        void reject() { is_rejected = true; }
+    };
+
+    static void visit(const ASTPtr & ast, Data & data)
+    {
+        if (data.is_rejected)
+            return;
+        if (const auto & identifier = ast->as<ASTIdentifier>())
+            visit(*identifier, data);
+    }
+
+    static void visit(const ASTIdentifier & ast, Data & data)
+    {
+        if (ast.getAliasOrColumnName() == data.alias)
+            data.reject();
+    }
+
+    static bool needChildVisit(const ASTPtr &, const ASTPtr &) { return true; }
+};
+
+using FunctionMaskingArgumentCheckVisitor = ConstInDepthNodeVisitor<FunctionMaskingArgumentCheckMatcher, false>;
+
+}

src/Interpreters/TreeOptimizer.cpp

@@ -13,6 +13,7 @@
 #include <Interpreters/AggregateFunctionOfGroupByKeysVisitor.h>
 #include <Interpreters/RewriteAnyFunctionVisitor.h>
 #include <Interpreters/RemoveInjectiveFunctionsVisitor.h>
+#include <Interpreters/FunctionMaskingArgumentCheckVisitor.h>
 #include <Interpreters/RedundantFunctionsInOrderByVisitor.h>
 #include <Interpreters/RewriteCountVariantsVisitor.h>
 #include <Interpreters/MonotonicityCheckVisitor.h>
@@ -153,6 +154,19 @@ void optimizeGroupBy(ASTSelectQuery * select_query, ContextPtr context)
                     continue;
                 }
             }
+            /// don't optimise functions that shadow any of it's arguments:
+            /// https://github.com/ClickHouse/ClickHouse/issues/37032
+            else if (!function->alias.empty())
+            {
+                FunctionMaskingArgumentCheckVisitor::Data data{.alias=function->alias};
+                FunctionMaskingArgumentCheckVisitor(data).visit(function->arguments);
+
+                if (data.is_rejected)
+                {
+                    ++i;
+                    continue;
+                }
+            }
 
             /// copy shared pointer to args in order to ensure lifetime
             auto args_ast = function->arguments;

tests/queries/0_stateless/02352_grouby_shadows_arg.reference

@@ -0,0 +1,6 @@
+0
+1
+4
+0
+1
+2

tests/queries/0_stateless/02352_grouby_shadows_arg.sql

@@ -0,0 +1,5 @@
+SET prefer_localhost_replica=0;
+SELECT toString(dummy) as dummy FROM remote('127.{1,1}', 'system.one') GROUP BY dummy;
+SELECT toString(dummy+1) as dummy FROM remote('127.{1,1}', 'system.one') GROUP BY dummy;
+SELECT toString((toInt8(dummy)+2) * (toInt8(dummy)+2)) as dummy FROM remote('127.{1,1}', system.one) GROUP BY dummy;
+SELECT round(number % 3) AS number FROM remote('127.{1,1}', numbers(20)) GROUP BY number ORDER BY number ASC;