add table function null

src/TableFunctions/TableFunctionNull.cpp

@@ -0,0 +1,42 @@
+#include <Interpreters/Context.h>
+#include <Parsers/ASTLiteral.h>
+#include <Parsers/ASTFunction.h>
+#include <Storages/StorageNull.h>
+#include <TableFunctions/parseColumnsListForTableFunction.h>
+#include <TableFunctions/ITableFunction.h>
+#include <TableFunctions/TableFunctionFactory.h>
+#include <TableFunctions/TableFunctionNull.h>
+#include "registerTableFunctions.h"
+
+
+namespace DB
+{
+namespace ErrorCodes
+{
+    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
+}
+
+StoragePtr TableFunctionNull::executeImpl(const ASTPtr & ast_function, const Context & context, const std::string & table_name) const
+{
+    if (const auto * function = ast_function->as<ASTFunction>())
+    {
+        auto arguments = function->arguments->children;
+
+        if (arguments.size() != 1)
+            throw Exception("Table function '" + getName() + "' requires 'structure'.", ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
+
+        auto structure = arguments[0]->as<ASTLiteral &>().value.safeGet<String>();
+        ColumnsDescription columns = parseColumnsListFromString(structure, context);
+
+        auto res = StorageNull::create(StorageID(getDatabaseName(), table_name), columns, ConstraintsDescription());
+        res->startup();
+        return res;
+    }
+    throw Exception("Table function '" + getName() + "' requires 'structure'.", ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
+}
+
+void registerTableFunctionNull(TableFunctionFactory & factory)
+{
+    factory.registerFunction<TableFunctionNull>();
+}
+}

src/TableFunctions/TableFunctionNull.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <TableFunctions/ITableFunction.h>
+#include <Core/Types.h>
+
+
+namespace DB
+{
+
+/* null(structure) - creates a temporary null storage
+ *
+ * Used for testing purposes, for convenience writing tests and demos.
+ */
+class TableFunctionNull : public ITableFunction
+{
+public:
+    static constexpr auto name = "null";
+    std::string getName() const override { return name; }
+private:
+    StoragePtr executeImpl(const ASTPtr & ast_function, const Context & context, const std::string & table_name) const override;
+    const char * getStorageTypeName() const override { return "Null"; }
+};
+
+}

src/TableFunctions/registerTableFunctions.cpp

@@ -11,6 +11,7 @@ void registerTableFunctions()
     registerTableFunctionMerge(factory);
     registerTableFunctionRemote(factory);
     registerTableFunctionNumbers(factory);
+    registerTableFunctionNull(factory);
     registerTableFunctionZeros(factory);
     registerTableFunctionFile(factory);
     registerTableFunctionURL(factory);

src/TableFunctions/registerTableFunctions.h

@@ -11,6 +11,7 @@ class TableFunctionFactory;
 void registerTableFunctionMerge(TableFunctionFactory & factory);
 void registerTableFunctionRemote(TableFunctionFactory & factory);
 void registerTableFunctionNumbers(TableFunctionFactory & factory);
+void registerTableFunctionNull(TableFunctionFactory & factory);
 void registerTableFunctionZeros(TableFunctionFactory & factory);
 void registerTableFunctionFile(TableFunctionFactory & factory);
 void registerTableFunctionURL(TableFunctionFactory & factory);