MySQL 8.0

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE t(id INT, col1 TEXT, col2 TEXt, col3 TEXT,
   col4 TEXT AS (concat_ws(',', col1, col2, col3))
   )
INSERT INTO t(id, col1, col2, col3)
VALUES 
(1, 'lorem', NULL, 'ipsum'),
(2, NULL, NULL, 'ipsum'),
(3, 'lorem', 'dolor', 'ipsum')
SELECT * FROM t


id
col1
col2
col3
col4


1
lorem
null
ipsum
lorem,ipsum

2
null
null
ipsum
ipsum

3
lorem
dolor
ipsum
lorem,dolor,ipsum

id	col1	col2	col3	col4
1	lorem	null	ipsum	lorem,ipsum
2	null	null	ipsum	ipsum
3	lorem	dolor	ipsum	lorem,dolor,ipsum