Add compat setting for sane NULL behavior in functions 'least' and 'greatest'

src/Core/Settings.cpp

@@ -3147,16 +3147,19 @@ Possible values:
 Allow execute multiIf function columnar
 )", 0) \
     DECLARE(Bool, formatdatetime_f_prints_single_zero, false, R"(
-Formatter '%f' in function 'formatDateTime()' prints a single zero instead of six zeros if the formatted value has no fractional seconds.
+Formatter '%f' in function 'formatDateTime' prints a single zero instead of six zeros if the formatted value has no fractional seconds.
 )", 0) \
     DECLARE(Bool, formatdatetime_parsedatetime_m_is_month_name, true, R"(
-Formatter '%M' in functions 'formatDateTime()' and 'parseDateTime()' print/parse the month name instead of minutes.
+Formatter '%M' in functions 'formatDateTime' and 'parseDateTime' print/parse the month name instead of minutes.
 )", 0) \
     DECLARE(Bool, parsedatetime_parse_without_leading_zeros, true, R"(
-Formatters '%c', '%l' and '%k' in function 'parseDateTime()' parse months and hours without leading zeros.
+Formatters '%c', '%l' and '%k' in function 'parseDateTime' parse months and hours without leading zeros.
 )", 0) \
     DECLARE(Bool, formatdatetime_format_without_leading_zeros, false, R"(
-Formatters '%c', '%l' and '%k' in function 'formatDateTime()' print months and hours without leading zeros.
+Formatters '%c', '%l' and '%k' in function 'formatDateTime' print months and hours without leading zeros.
+)", 0) \
+    DECLARE(Bool, least_greatest_legacy_null_behavior, false, R"(
+If enabled, functions 'least' and 'greatest' return NULL if one of their arguments is NULL.
 )", 0) \
     \
     DECLARE(UInt64, max_partitions_per_insert_block, 100, R"(

src/Core/SettingsChangesHistory.cpp

@@ -79,6 +79,7 @@ static std::initializer_list<std::pair<ClickHouseVersion, SettingsChangesHistory
             {"http_response_headers", "", "", "New setting."},
             {"skip_redundant_aliases_in_udf", false, false, "New setting."},
             {"parallel_replicas_index_analysis_only_on_coordinator", true, true, "Index analysis done only on replica-coordinator and skipped on other replicas. Effective only with enabled parallel_replicas_local_plan"}, // enabling it was moved to 24.10
+            {"least_greatest_legacy_null_behavior", false, false, "New setting"},
             /// Release closed. Please use 25.1
         }
     },

src/Functions/LeastGreatestGeneric.h

@@ -2,8 +2,10 @@
 
 #include <DataTypes/getLeastSupertype.h>
 #include <DataTypes/NumberTraits.h>
+#include <Interpreters/Context.h>
 #include <Interpreters/castColumn.h>
 #include <Columns/ColumnsNumber.h>
+#include <Core/Settings.h>
 #include <Functions/IFunction.h>
 #include <Functions/FunctionFactory.h>
 #include <base/map.h>
@@ -11,6 +13,11 @@
 namespace DB
 {
 
+namespace Setting
+{
+    extern const SettingsBool least_greatest_legacy_null_behavior;
+}
+
 namespace ErrorCodes
 {
     extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
@@ -29,14 +36,21 @@ class FunctionLeastGreatestGeneric : public IFunction
 {
 public:
     static constexpr auto name = kind == LeastGreatest::Least ? "least" : "greatest";
-    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionLeastGreatestGeneric<kind>>(); }
+    static FunctionPtr create(ContextPtr context) { return std::make_shared<FunctionLeastGreatestGeneric<kind>>(context); }
+
+    /// TODO Remove support for legacy NULL behavior (can be done end of 2026)
+
+    explicit FunctionLeastGreatestGeneric(ContextPtr context)
+        : legacy_null_behavior(context->getSettingsRef()[Setting::least_greatest_legacy_null_behavior])
+    {
+    }
 
 private:
     String getName() const override { return name; }
     size_t getNumberOfArguments() const override { return 0; }
     bool isVariadic() const override { return true; }
     bool useDefaultImplementationForConstants() const override { return true; }
-    bool useDefaultImplementationForNulls() const override { return false; }
+    bool useDefaultImplementationForNulls() const override { return legacy_null_behavior; }
     bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
 
     DataTypePtr getReturnTypeImpl(const DataTypes & types) const override
@@ -55,15 +69,15 @@ private:
         Columns converted_columns;
         for (const auto & argument : arguments)
         {
-            if (argument.type->onlyNull())
+            if (!legacy_null_behavior && argument.type->onlyNull())
                 continue; /// ignore NULL arguments
             auto converted_col = castColumn(argument, result_type)->convertToFullColumnIfConst();
-            converted_columns.emplace_back(converted_col);
+            converted_columns.push_back(converted_col);
         }
 
-        if (converted_columns.empty())
+        if (!legacy_null_behavior && converted_columns.empty())
             return arguments[0].column;
-        else if (converted_columns.size() == 1)
+        else if (!legacy_null_behavior && converted_columns.size() == 1)
             return converted_columns[0];
 
         auto result_column = result_type->createColumn();
@@ -93,6 +107,8 @@ private:
 
         return result_column;
     }
+
+    bool legacy_null_behavior;
 };
 
 template <LeastGreatest kind, typename SpecializedFunction>
@@ -100,18 +116,18 @@ class LeastGreatestOverloadResolver : public IFunctionOverloadResolver
 {
 public:
     static constexpr auto name = kind == LeastGreatest::Least ? "least" : "greatest";
+    static FunctionOverloadResolverPtr create(ContextPtr context) { return std::make_unique<LeastGreatestOverloadResolver<kind, SpecializedFunction>>(context); }
 
-    static FunctionOverloadResolverPtr create(ContextPtr context)
+    explicit LeastGreatestOverloadResolver(ContextPtr context_)
+        : context(context_)
+        , legacy_null_behavior(context->getSettingsRef()[Setting::least_greatest_legacy_null_behavior])
     {
-        return std::make_unique<LeastGreatestOverloadResolver<kind, SpecializedFunction>>(context);
     }
 
-    explicit LeastGreatestOverloadResolver(ContextPtr context_) : context(context_) {}
-
     String getName() const override { return name; }
     size_t getNumberOfArguments() const override { return 0; }
     bool isVariadic() const override { return true; }
-    bool useDefaultImplementationForNulls() const override { return false; }
+    bool useDefaultImplementationForNulls() const override { return legacy_null_behavior; }
 
     FunctionBasePtr buildImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr & return_type) const override
     {
@@ -120,8 +136,13 @@ public:
             argument_types.push_back(argument.type);
 
         /// More efficient specialization for two numeric arguments.
-        if (arguments.size() == 2 && isNumber(arguments[0].type) && isNumber(arguments[1].type))
+        if (arguments.size() == 2)
-            return std::make_unique<FunctionToFunctionBaseAdaptor>(SpecializedFunction::create(context), argument_types, return_type);
+        {
+            auto arg_0_type = legacy_null_behavior ? removeNullable(arguments[0].type) : arguments[0].type;
+            auto arg_1_type = legacy_null_behavior ? removeNullable(arguments[1].type) : arguments[1].type;
+            if (isNumber(arg_0_type) && isNumber(arg_1_type))
+                return std::make_unique<FunctionToFunctionBaseAdaptor>(SpecializedFunction::create(context), argument_types, return_type);
+        }
 
         return std::make_unique<FunctionToFunctionBaseAdaptor>(
             FunctionLeastGreatestGeneric<kind>::create(context), argument_types, return_type);
@@ -132,14 +153,20 @@ public:
         if (types.empty())
             throw Exception(ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH, "Function {} cannot be called without arguments", getName());
 
-        if (types.size() == 2 && isNumber(types[0]) && isNumber(types[1]))
+        if (types.size() == 2)
-            return SpecializedFunction::create(context)->getReturnTypeImpl(types);
+        {
+            auto arg_0_type = legacy_null_behavior ? removeNullable(types[0]) : types[0];
+            auto arg_1_type = legacy_null_behavior ? removeNullable(types[1]) : types[1];
+            if (isNumber(arg_0_type) && isNumber(arg_1_type))
+                return SpecializedFunction::create(context)->getReturnTypeImpl(types);
+        }
 
         return getLeastSupertype(types);
     }
 
 private:
     ContextPtr context;
+    bool legacy_null_behavior;
 };
 
 }

tests/queries/0_stateless/03174_least_greatest_ignore_null_input_values.reference

@@ -1,3 +1,4 @@
+Test with default NULL behavior
 Test with one const argument
 \N	\N
 Test with two const arguments
@@ -19,3 +20,25 @@ a	a
 Special cases
 2	1
 1	1
+Repeat above tests with legacy NULL behavior
+Test with one const argument
+\N	\N
+Test with two const arguments
+\N	\N
+\N	\N
+\N	\N
+\N	\N
+\N	\N
+\N	\N
+Test with one non-const argument
+\N	\N
+Test with two non-const arguments
+\N	\N
+\N	\N
+\N	\N
+\N	\N
+\N	\N
+\N	\N
+Special cases
+2	1
+\N	\N

tests/queries/0_stateless/03174_least_greatest_ignore_null_input_values.sql

@@ -1,5 +1,39 @@
 -- Tests functions "greatest" and "least" with NULL arguments
 
+SELECT 'Test with default NULL behavior';
+SET least_greatest_legacy_null_behavior = default;
+
+SELECT 'Test with one const argument';
+SELECT greatest(NULL), least(NULL);
+
+SELECT 'Test with two const arguments';
+SELECT greatest(1, NULL), least(1, NULL);
+SELECT greatest(NULL, 1), least(NULL, 1);
+SELECT greatest(NULL, 1.1), least(NULL, 1.1);
+SELECT greatest(1.1, NULL), least(1.1, NULL);
+SELECT greatest(NULL, 'a'), least(NULL, 'a');
+SELECT greatest('a', NULL), least('a', NULL);
+
+SELECT 'Test with one non-const argument';
+SELECT greatest(materialize(NULL)), least(materialize(NULL));
+
+SELECT 'Test with two non-const arguments';
+SELECT greatest(materialize(1), NULL), least(materialize(1), NULL);
+SELECT greatest(materialize(NULL), 1), least(materialize(NULL), 1);
+SELECT greatest(materialize(NULL), 1.1), least(materialize(NULL), 1.1);
+SELECT greatest(materialize(1.1), NULL), least(materialize(1.1), NULL);
+SELECT greatest(materialize(NULL), 'a'), least(materialize(NULL), 'a');
+SELECT greatest(materialize('a'), NULL), least(materialize('a'), NULL);
+
+SELECT 'Special cases';
+SELECT greatest(toNullable(1), 2), least(toNullable(1), 2);
+SELECT greatest(toLowCardinality(1), NULL), least(toLowCardinality(1), NULL);
+
+-- ----------------------------------------------------------------------------
+
+SELECT 'Repeat above tests with legacy NULL behavior';
+SET least_greatest_legacy_null_behavior = true;
+
 SELECT 'Test with one const argument';
 SELECT greatest(NULL), least(NULL);