From 234367b0382a46e5a023594df7a779983770cfde Mon Sep 17 00:00:00 2001
From: Alexey Milovidov <milovidov@yandex-team.ru>
Date: Tue, 14 Jul 2015 00:27:08 +0300
Subject: [PATCH] dbms: added function identity [#METR-17251].

---
 .../DB/Functions/FunctionsMiscellaneous.h     | 30 +++++++++++++++++++
 dbms/src/Functions/FunctionsMiscellaneous.cpp |  1 +
 .../0_stateless/00194_identity.reference      |  1 +
 .../queries/0_stateless/00194_identity.sql    |  1 +
 4 files changed, 33 insertions(+)
 create mode 100644 dbms/tests/queries/0_stateless/00194_identity.reference
 create mode 100644 dbms/tests/queries/0_stateless/00194_identity.sql

diff --git a/dbms/include/DB/Functions/FunctionsMiscellaneous.h b/dbms/include/DB/Functions/FunctionsMiscellaneous.h
index 06320362501..ae606f53182 100644
--- a/dbms/include/DB/Functions/FunctionsMiscellaneous.h
+++ b/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:
diff --git a/dbms/src/Functions/FunctionsMiscellaneous.cpp b/dbms/src/Functions/FunctionsMiscellaneous.cpp
index e2a478933c1..08b51f8ba5f 100644
--- a/dbms/src/Functions/FunctionsMiscellaneous.cpp
+++ b/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>();
diff --git a/dbms/tests/queries/0_stateless/00194_identity.reference b/dbms/tests/queries/0_stateless/00194_identity.reference
new file mode 100644
index 00000000000..72749c905a3
--- /dev/null
+++ b/dbms/tests/queries/0_stateless/00194_identity.reference
@@ -0,0 +1 @@
+1	1	1
diff --git a/dbms/tests/queries/0_stateless/00194_identity.sql b/dbms/tests/queries/0_stateless/00194_identity.sql
new file mode 100644
index 00000000000..cb2e7264b16
--- /dev/null
+++ b/dbms/tests/queries/0_stateless/00194_identity.sql
@@ -0,0 +1 @@
+SELECT identity(1 AS a) AS b, a, b;