SQL query on SUM function plus JOINS Sorry if this has been covered before but I couldnt find an example to my issue

Situation: Say I have a table of sales and want to display them

Step 1)

SELECT payment_id, amount, payment_date
FROM payment
WHERE payment_date &gt;= '2018-01-01' 
AND payment_date &lt;= NOW());


Now I want to sum sales or 'amount
Step 2)

SELECT SUM(amount) as 'Total Amount'
FROM
(SELECT payment_id, amount, payment_date
FROM payment
WHERE payment_date &gt;= '2018-01-01' 
AND payment_date &lt;= NOW()
);


Is it possible to have that 'total amount' as a new row in my first table? Ie join the list of payment details with a total amount figure at the end of the list?
As I understand payment_id is unique (maybe primary). If so:

SELECT payment_id, SUM(amount), payment_date
FROM payment
WHERE payment_date &gt;= '2018-01-01' 
AND payment_date &lt;= NOW())
GROUP BY payment_id WITH ROLLUP;


If it is not unique, or if ONLY_FULL_GROUP_BY enabled:

SELECT payment_id, SUM(amount), payment_date
FROM payment
WHERE payment_date &gt;= '2018-01-01' 
AND payment_date &lt;= NOW())
GROUP BY payment_id, payment_date WITH ROLLUP
HAVING payment_date IS NOT NULL or payment_id IS NULL;


Last query will give wrong result if payment_date can be NULL.