dbms: added function identity [#METR-17251].

dbms/include/DB/Functions/FunctionsMiscellaneous.h

@@ -534,6 +534,36 @@ public:
 };
 
 
+class FunctionIdentity : public IFunction
+{
+public:
+	static constexpr auto name = "identity";
+	static IFunction * create(const Context & context) { return new FunctionIdentity; }
+
+	/// Получить имя функции.
+	String getName() const
+	{
+		return name;
+	}
+
+	/// Получить тип результата по типам аргументов. Если функция неприменима для данных аргументов - кинуть исключение.
+	DataTypePtr getReturnType(const DataTypes & arguments) const
+	{
+		if (arguments.size() != 1)
+			throw Exception("Function " + getName() + " requires exactly one argument.",
+				ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
+
+		return arguments.front()->clone();
+	}
+
+	/// Выполнить функцию над блоком.
+	void execute(Block & block, const ColumnNumbers & arguments, size_t result)
+	{
+		block.getByPosition(result).column = block.getByPosition(arguments.front()).column;
+	}
+};
+
+
 class FunctionArrayJoin : public IFunction
 {
 public:

dbms/src/Functions/FunctionsMiscellaneous.cpp

@@ -325,6 +325,7 @@ void registerFunctionsMiscellaneous(FunctionFactory & factory)
 	factory.registerFunction<FunctionSleep>();
 	factory.registerFunction<FunctionMaterialize>();
 	factory.registerFunction<FunctionIgnore>();
+	factory.registerFunction<FunctionIdentity>();
 	factory.registerFunction<FunctionArrayJoin>();
 	factory.registerFunction<FunctionReplicate>();
 	factory.registerFunction<FunctionBar>();

dbms/tests/queries/0_stateless/00194_identity.reference

+1	1	1

dbms/tests/queries/0_stateless/00194_identity.sql

+SELECT identity(1 AS a) AS b, a, b;