diff --git a/dbms/src/Functions/FunctionsNull.cpp b/dbms/src/Functions/FunctionsNull.cpp
index 131bf4280c3..09f583fdcf4 100644
--- a/dbms/src/Functions/FunctionsNull.cpp
+++ b/dbms/src/Functions/FunctionsNull.cpp
@@ -190,6 +190,15 @@ std::string FunctionIfNull::getName() const
 	return name;
 }
 
+
+static const DataTypePtr getNestedDataType(const DataTypePtr & type)
+{
+	if (type->isNullable())
+		return static_cast<const DataTypeNullable &>(*type).getNestedType();
+
+	return type;
+}
+
 bool FunctionIfNull::hasSpecialSupportForNulls() const
 {
 	return true;
@@ -197,20 +206,29 @@ bool FunctionIfNull::hasSpecialSupportForNulls() const
 
 DataTypePtr FunctionIfNull::getReturnTypeImpl(const DataTypes & arguments) const
 {
-	return FunctionIf{}.getReturnTypeImpl({std::make_shared<DataTypeUInt8>(), arguments[0], arguments[1]});
+	if (arguments[0]->isNull())
+		return arguments[1];
+
+	return FunctionIf{}.getReturnTypeImpl({std::make_shared<DataTypeUInt8>(), getNestedDataType(arguments[0]), arguments[1]});
 }
 
 void FunctionIfNull::executeImpl(Block & block, const ColumnNumbers & arguments, size_t result)
 {
-	/// ifNull(col1, col2) == multiIf(isNotNull(col1), col1, col2)
+	if (block.getByPosition(arguments[0]).column->isNull())
+		block.getByPosition(result).column = block.getByPosition(arguments[1]).column;
+
+	/// ifNull(col1, col2) == if(isNotNull(col1), assumeNotNull(col1), col2)
 
 	Block temp_block = block;
 
-	size_t res_pos = temp_block.columns();
+	size_t is_not_null_pos = temp_block.columns();
 	temp_block.insert({nullptr, std::make_shared<DataTypeUInt8>(), ""});
+	size_t assume_not_null_pos = temp_block.columns();
+	temp_block.insert({nullptr, getNestedDataType(block.getByPosition(arguments[0]).type), ""});
 
-	FunctionIsNotNull{}.executeImpl(temp_block, {arguments[0]}, res_pos);
-	FunctionIf{}.executeImpl(temp_block, {res_pos, arguments[0], arguments[1]}, result);
+	FunctionIsNotNull{}.executeImpl(temp_block, {arguments[0]}, is_not_null_pos);
+	FunctionAssumeNotNull{}.executeImpl(temp_block, {arguments[0]}, assume_not_null_pos);
+	FunctionIf{}.executeImpl(temp_block, {is_not_null_pos, assume_not_null_pos, arguments[1]}, result);
 
 	block.safeGetByPosition(result).column = std::move(temp_block.safeGetByPosition(result).column);
 }
@@ -285,13 +303,7 @@ DataTypePtr FunctionAssumeNotNull::getReturnTypeImpl(const DataTypes & arguments
 {
 	if (arguments[0]->isNull())
 		throw Exception{"NULL is an invalid value for function " + getName(), ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT};
-	else if (arguments[0]->isNullable())
-	{
-		const DataTypeNullable & nullable_type = static_cast<const DataTypeNullable &>(*arguments[0]);
-		return nullable_type.getNestedType();
-	}
-	else
-		return arguments[0];
+	return getNestedDataType(arguments[0]);
 }
 
 void FunctionAssumeNotNull::executeImpl(Block & block, const ColumnNumbers & arguments, size_t result)