Use FunctionFactory to invoke dateName

src/Functions/monthName.cpp

@@ -0,0 +1,77 @@
+#include <Columns/ColumnString.h>
+#include <DataTypes/DataTypeString.h>
+#include <IO/WriteHelpers.h>
+#include <Functions/FunctionFactory.h>
+
+namespace DB
+{
+namespace ErrorCodes
+{
+    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
+    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
+}
+
+class FunctionMonthNameImpl : public IFunction
+{
+public:
+    static constexpr auto name = "monthName";
+
+    static constexpr auto month_str = "month";
+
+    static FunctionPtr create(ContextPtr context) { return std::make_shared<FunctionMonthNameImpl>(context); }
+
+    explicit FunctionMonthNameImpl(ContextPtr context_) : context(context_) {}
+
+    String getName() const override { return name; }
+
+    bool useDefaultImplementationForConstants() const override { return true; }
+
+    bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
+
+    size_t getNumberOfArguments() const override { return 1; }
+
+    DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
+    {
+        if (arguments.size() != 1)
+            throw Exception(
+                ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH,
+                "Number of arguments for function {} doesn't match: passed {}, should be 1",
+                getName(),
+                toString(arguments.size()));
+
+        WhichDataType argument_type(arguments[0].type);
+        if (!argument_type.isDate() && !argument_type.isDateTime() && !argument_type.isDateTime64())
+            throw Exception(
+                ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT,
+                "Illegal type of argument of function {}, should be Date, DateTime or DateTime64",
+                getName());
+
+        return std::make_shared<DataTypeString>();
+    }
+
+    ColumnPtr executeImpl(
+        const ColumnsWithTypeAndName & arguments,
+        const DataTypePtr & result_type,
+        [[maybe_unused]] size_t input_rows_count) const override
+    {
+        auto month_column = DataTypeString().createColumnConst(arguments[0].column->size(), month_str);
+        ColumnsWithTypeAndName temporary_columns
+        {
+            ColumnWithTypeAndName(month_column, std::make_shared<DataTypeString>(), ""),
+            arguments[0]
+        };
+
+        auto dateName = FunctionFactory::instance().get("dateName", context)->build(temporary_columns);
+        return dateName->execute(temporary_columns, result_type, input_rows_count);
+    }
+
+private:
+    ContextPtr context;
+};
+
+void registerFunctionMonthName(FunctionFactory & factory)
+{
+    factory.registerFunction<FunctionMonthNameImpl>(FunctionFactory::CaseInsensitive);
+}
+
+}

src/Functions/registerFunctionsDateTime.cpp

@@ -65,6 +65,7 @@ void registerFunctionSubtractQuarters(FunctionFactory &);
 void registerFunctionSubtractYears(FunctionFactory &);
 void registerFunctionDateDiff(FunctionFactory &);
 void registerFunctionDateName(FunctionFactory &);
+void registerFunctionMonthName(FunctionFactory &);
 void registerFunctionToTimeZone(FunctionFactory &);
 void registerFunctionFormatDateTime(FunctionFactory &);
 void registerFunctionFromModifiedJulianDay(FunctionFactory &);
@@ -136,6 +137,7 @@ void registerFunctionsDateTime(FunctionFactory & factory)
     registerFunctionSubtractYears(factory);
     registerFunctionDateDiff(factory);
     registerFunctionDateName(factory);
+    registerFunctionMonthName(factory);
     registerFunctionToTimeZone(factory);
     registerFunctionFormatDateTime(factory);
     registerFunctionFromModifiedJulianDay(factory);