dbms: function 'transform': added support for constant argument [#METR-15987].

dbms/include/DB/Functions/FunctionsMiscellaneous.h

@@ -1003,6 +1003,13 @@ public:
 		prepare(array_from->getData(), array_to->getData(), block, arguments);
 
 		const auto in = block.getByPosition(arguments.front()).column.get();
+
+		if (in->isConst())
+		{
+			executeConst(block, arguments, result);
+			return;
+		}
+
 		auto column_result = block.getByPosition(result).type->createColumn();
 		auto out = column_result.get();
 
@@ -1024,6 +1031,34 @@ public:
 		block.getByPosition(result).column = column_result;
 	}
 
+private:
+	void executeConst(Block & block, const ColumnNumbers & arguments, const size_t result)
+	{
+		/// Составим блок из полноценных столбцов размера 1 и вычислим функцию как обычно.
+
+		Block tmp_block;
+		ColumnNumbers tmp_arguments;
+
+		tmp_block.insert(block.getByPosition(arguments[0]));
+		tmp_block.getByPosition(0).column = static_cast<IColumnConst *>(tmp_block.getByPosition(0).column->cloneResized(1).get())->convertToFullColumn();
+		tmp_arguments.push_back(0);
+
+		for (size_t i = 1; i < arguments.size(); ++i)
+		{
+			tmp_block.insert(block.getByPosition(arguments[i]));
+			tmp_arguments.push_back(i);
+		}
+
+		tmp_block.insert(block.getByPosition(result));
+		size_t tmp_result = arguments.size();
+
+		execute(tmp_block, tmp_arguments, tmp_result);
+
+		block.getByPosition(result).column = block.getByPosition(result).type->createConstColumn(
+			block.rowsInFirstColumn(),
+			(*tmp_block.getByPosition(tmp_result).column)[0]);
+	}
+
 	template <typename T>
 	bool executeNum(const IColumn * in_untyped, IColumn * out_untyped)
 	{
@@ -1060,12 +1095,6 @@ public:
 
 			return true;
 		}
-		else if (const auto in = typeid_cast<const ColumnConst<T> *>(in_untyped))
-		{
-			/* TODO */
-
-			return true;
-		}
 
 		return false;
 	}
@@ -1091,12 +1120,6 @@ public:
 
 			return true;
 		}
-		else if (const auto in = typeid_cast<const ColumnConstString *>(in_untyped))
-		{
-			/* TODO */
-
-			return true;
-		}
 
 		return false;
 	}
@@ -1252,7 +1275,7 @@ public:
 		}
 	}
 
-private:
+
 	/// Разные варианты хэш-таблиц для реализации отображения.
 
 	using NumToNum = HashMap<UInt64, UInt64, HashCRC32<UInt64>>;
@@ -1298,6 +1321,10 @@ private:
 		if (arguments.size() == 4)
 		{
 			const IColumnConst * default_col = dynamic_cast<const IColumnConst *>(&*block.getByPosition(arguments[3]).column);
+
+			if (!default_col)
+				throw Exception("Fourth argument of function " + getName() + " (default value) must be constant", ErrorCodes::ILLEGAL_COLUMN);
+
 			default_value = (*default_col)[0];
 
 			/// Нужно ли преобразовать элементы to и default_value к наименьшему общему типу, который является Float64?

dbms/tests/queries/0_stateless/00153_transform.reference

@@ -98,3 +98,7 @@ abc
 333
 1
 1
+Остальные
+Яндекс
+Google
+Остальные

dbms/tests/queries/0_stateless/00153_transform.sql

@@ -8,3 +8,7 @@ SELECT transform(toString(number), ['3', '5', '7'], [111, 222, 333], 0) FROM sys
 SELECT transform(toString(number), ['3', '5', '7'], [111, 222, 333], -1) FROM system.numbers LIMIT 10;
 SELECT transform(toString(number), ['3', '5', '7'], [111, 222, 333], -1.1) FROM system.numbers LIMIT 10;
 SELECT transform(toString(number), ['3', '5', '7'], [111, 222.2, 333], 1) FROM system.numbers LIMIT 10;
+SELECT transform(1, [2, 3], ['Яндекс', 'Google'], 'Остальные') AS title;
+SELECT transform(2, [2, 3], ['Яндекс', 'Google'], 'Остальные') AS title;
+SELECT transform(3, [2, 3], ['Яндекс', 'Google'], 'Остальные') AS title;
+SELECT transform(4, [2, 3], ['Яндекс', 'Google'], 'Остальные') AS title;