Fix *If combinator with Nullable types

sumIf(Nullable()) and similar unary functions (unary w/o If combinator)
was working incorrectly, since it returns "sum" from the getName()
helper, and so distributed query processing fails.

The problem is in the optimization in
AggregateFunctionIfNullUnary::add() for the unary functions. It pass
only one column to write result to, instead of all passed arguments +
result columns.
While AggregateFunctionIf::add() assumes that it accepts arguments  +
result columns, and use last column as a result.

Introduced-in: #16610
Fixes: #18210

src/AggregateFunctions/AggregateFunctionIf.cpp

@@ -53,17 +53,35 @@ class AggregateFunctionIfNullUnary final
 private:
     size_t num_arguments;
 
+    /// The name of the nested function, including combinators (i.e. *If)
+    ///
+    /// getName() from the nested_function cannot be used because in case of *If combinator
+    /// with Nullable argument nested_function will point to the function w/o combinator.
+    /// (I.e. sumIf(Nullable, 1) -> sum()), and distributed query processing will fail.
+    ///
+    /// And nested_function cannot point to the function with *If since
+    /// due to optimization in the add() which pass only one column with the result,
+    /// and so AggregateFunctionIf::add() cannot be called this way
+    /// (it write to the last argument -- num_arguments-1).
+    ///
+    /// And to avoid extra level of indirection, the name of function is cached:
+    ///
+    ///     AggregateFunctionIfNullUnary::add -> [ AggregateFunctionIf::add -> ] AggregateFunctionSum::add
+    String name;
+
     using Base = AggregateFunctionNullBase<result_is_nullable, serialize_flag,
         AggregateFunctionIfNullUnary<result_is_nullable, serialize_flag>>;
 public:
 
     String getName() const override
     {
-        return Base::getName();
+        return name;
     }
 
-    AggregateFunctionIfNullUnary(AggregateFunctionPtr nested_function_, const DataTypes & arguments, const Array & params)
+    AggregateFunctionIfNullUnary(const String & name_, AggregateFunctionPtr nested_function_, const DataTypes & arguments, const Array & params)
-        : Base(std::move(nested_function_), arguments, params), num_arguments(arguments.size())
+        : Base(std::move(nested_function_), arguments, params)
+        , num_arguments(arguments.size())
+        , name(name_)
     {
         if (num_arguments == 0)
             throw Exception("Aggregate function " + getName() + " require at least one argument",
@@ -174,14 +192,14 @@ AggregateFunctionPtr AggregateFunctionIf::getOwnNullAdapter(
     {
         if (return_type_is_nullable)
         {
-            return std::make_shared<AggregateFunctionIfNullUnary<true, true>>(nested_func, arguments, params);
+            return std::make_shared<AggregateFunctionIfNullUnary<true, true>>(nested_function->getName(), nested_func, arguments, params);
         }
         else
         {
             if (serialize_flag)
-                return std::make_shared<AggregateFunctionIfNullUnary<false, true>>(nested_func, arguments, params);
+                return std::make_shared<AggregateFunctionIfNullUnary<false, true>>(nested_function->getName(), nested_func, arguments, params);
             else
-                return std::make_shared<AggregateFunctionIfNullUnary<false, false>>(nested_func, arguments, params);
+                return std::make_shared<AggregateFunctionIfNullUnary<false, false>>(nested_function->getName(), nested_func, arguments, params);
         }
     }
     else

tests/queries/0_stateless/01642_if_nullable_regression.reference

@@ -0,0 +1,5 @@
+\N
+\N
+\N
+0
+90

tests/queries/0_stateless/01642_if_nullable_regression.sql

@@ -0,0 +1,7 @@
+SELECT sumIf(dummy, dummy) FROM remote('127.0.0.{1,2}', view(SELECT cast(Null  AS Nullable(UInt8))  AS dummy FROM system.one));
+SELECT sumIf(dummy, 1)     FROM remote('127.0.0.{1,2}', view(SELECT cast(Null  AS Nullable(UInt8))  AS dummy FROM system.one));
+-- Before #16610 it returns 0 while with this patch it will return NULL
+SELECT sumIf(dummy, dummy) FROM remote('127.0.0.{1,2}', view(SELECT cast(dummy AS Nullable(UInt8)) AS dummy FROM system.one));
+SELECT sumIf(dummy, 1)     FROM remote('127.0.0.{1,2}', view(SELECT cast(dummy AS Nullable(UInt8)) AS dummy FROM system.one));
+
+SELECT sumIf(n, 1) FROM remote('127.0.0.{1,2}', view(SELECT cast(* AS Nullable(UInt8)) AS n FROM system.numbers limit 10))