SQL - better way to group and sum based on condition

Question

I have data like:

Year	Amount
2001	1
2020	2
2020	2
2021	5
2022	2
2022	2
2021	2

And I want to summarise data like:

Year	Amount
2020 and before	5
2021	7
2022	4

I thought of 2 ways, and want to see whether there are any better method.

1. Use Union

Select Year, sum(Amount) from TABLE_A 
where Year <= 2020
UNION
Select Year, sum(Amount) from TABLE_A 
where Year > 2020

2. Added a new column

SELECT YR, SUM(Amount) FROM
(
  SELECT CASE WHEN Year <= 2020 THEN '2020_and_before') ELSE Year END as YR, * 
  FROM TABLE_A ) A
GROUP BY YR

I can get the results I want, but want to see whether there is better method

Answer 1

In MySQL, you can avoid subqueries with a CASE expression in the following way:

SELECT CASE WHEN Year_ <= 2020 THEN "2020 or before"
            ELSE Year_ END AS Year_ ,
       SUM(Amount) AS total_amount
FROM tab       
GROUP BY 1

Output:

Year_	total_amount
2020 or before	5
2021	7
2022	4

Check a MySQL demo here .

Note : You should avoid messing with data types. If you're supposed to store years in the year field, you could leave the integer 2020, instead of having a string like "2020 or before".