CASE，当column1为NULL时则为NULL ELSE column2结束

Question

I am simply fetching total number of upvote in comment table, but want the last row to print NULL in the content column.

Following is the simple query I am trying to run:

SELECT
    id
    , content -- THIS IS JUST TO COMPARE, WE DON'T NEED THIS
    , (CASE WHEN id IS NULL THEN NULL ELSE content END) as editedContent -- WE NEED THIS(WITH NULL VALUE IN THE END)
    , SUM(upvote)
FROM `test`.`comment`
GROUP BY id WITH ROLLUP

OUTPUT:

+------+-------------+---------------+-------------+
| id   | content     | editedContent | SUM(upvote) |
+------+-------------+---------------+-------------+
| 26   | Content13-2 | Content14-1   |           2 |
| 27   | Content14-1 | Content14-2   |           2 |
| 28   | Content14-2 | Content15-1   |           2 |
| 29   | Content15-1 | Content15-2   |           3 |
| 30   | Content15-2 | Content15-2   |           2 |
| NULL | Content15-2 | Content15-2   |          55 |
+------+-------------+---------------+-------------+
6 rows in set (0.00 sec)

Expected Output:

+------+-------------+---------------+-------------+
| id   | content     | editedContent | SUM(upvote) |
+------+-------------+---------------+-------------+
| 26   | Content13-2 | Content13-2   |           2 |
| 27   | Content14-1 | Content14-1   |           2 |
| 28   | Content14-2 | Content14-2   |           2 |
| 29   | Content15-1 | Content15-1   |           3 |
| 30   | Content15-2 | Content15-2   |           2 |
| NULL | Content15-2 | NULL          |          55 |
+------+-------------+---------------+-------------+
6 rows in set (0.00 sec)

Answer 1

Try following,

SELECT
    id
    , content -- THIS IS JUST TO COMPARE, WE DON'T NEED THIS
    , (CASE WHEN id IS NULL THEN NULL ELSE content END) as editedContent -- WE NEED THIS(WITH NULL VALUE IN THE END)
    , SUM(upvote)
FROM `test`.`comment`
GROUP BY id 

Union all

select 
    'null',
    'null',
    'null',
    SUM(upvote)
from comment

Answer 2

try this query

SELECT
    id
    , content -- THIS IS JUST TO COMPARE, WE DON'T NEED THIS
    , (CASE WHEN id IS NULL THEN id ELSE content END) as editedContent -- WE NEED THIS(WITH NULL VALUE IN THE END)
    , SUM(upvote)
FROM `test`.`comment`
GROUP BY id WITH ROLLUP