Method executeImpl

src/Functions/if.cpp:1376–1483

    }

    ColumnPtr executeImpl(const ColumnsWithTypeAndName & args, const DataTypePtr & result_type, size_t input_rows_count) const override
    {
        ColumnsWithTypeAndName arguments = args;
        executeShortCircuitArguments(arguments);
        ColumnPtr res;
        if (   (res = executeForConstAndNullableCondition(arguments, result_type, input_rows_count))
            || (res = executeForNullThenElse(arguments, result_type, input_rows_count))
            || (res = executeForNullableThenElse(arguments, result_type, input_rows_count)))
            return res;

        const ColumnWithTypeAndName & arg_cond = arguments[0];
        const ColumnWithTypeAndName & arg_then = arguments[1];
        const ColumnWithTypeAndName & arg_else = arguments[2];

        /// A case for identical then and else (pointers are the same).
        if (arg_then.column.get() == arg_else.column.get())
        {
            /// Just point result to them.
            return arg_then.column;
        }

        const ColumnUInt8 * cond_col = typeid_cast<const ColumnUInt8 *>(arg_cond.column.get());
        const ColumnConst * cond_const_col = checkAndGetColumnConst<ColumnVector<UInt8>>(arg_cond.column.get());
        ColumnPtr materialized_cond_col;

        if (cond_const_col)
        {
            UInt8 value = cond_const_col->getValue<UInt8>();
            const ColumnWithTypeAndName & arg = value ? arg_then : arg_else;
            if (arg.type->equals(*result_type))
                return arg.column;
            return castForIf(arg, result_type);
        }

        if (!cond_col)
            throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Illegal column {} of first argument of function {}. "
                "Must be ColumnUInt8 or ColumnConstUInt8.", arg_cond.column->getName(), getName());

        /// If result is Variant, always use generic implementation.
        /// Using typed implementations may lead to incorrect result column type when
        /// resulting Variant is created by use_variant_when_no_common_type.
        if (isVariant(result_type))
            return executeGeneric(cond_col, arguments, result_type, input_rows_count);

        auto call = [&](const auto & types) -> bool
        {
            using Types = std::decay_t<decltype(types)>;
            using T0 = typename Types::LeftType;
            using T1 = typename Types::RightType;

            res = executeTyped<T0, T1>(cond_col, arguments, result_type, input_rows_count);
            return res != nullptr;
        };

        DataTypePtr left_type = arg_then.type;
        DataTypePtr right_type = arg_else.type;

        if (const auto * left_array = checkAndGetDataType<DataTypeArray>(arg_then.type.get()))