MySQL 5.7

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select version();


version()


5.7.39


DROP TABLE IF EXISTS `posts`;
CREATE TABLE IF NOT EXISTS `posts` (
  `id` INTEGER,
  `comments` JSON NOT NULL
);
INSERT INTO `posts` (`id`, `comments`) VALUES
(
    1,
    JSON_ARRAY(
        JSON_OBJECT('at', NOW(), 'content', 'Post #1 - Comment #1'),
        JSON_OBJECT('at', NOW(), 'content', 'Post #1 - Comment #2'),
        JSON_OBJECT('at', NOW(), 'content', 'Post #1 - Comment #3'),
        JSON_OBJECT('at', NOW(), 'content', 'Post #1 - Comment #4'),
        JSON_OBJECT('at', NOW(), 'content', 'Post #1 - Comment #5'),
        JSON_OBJECT('at', NOW(), 'content', 'Post #1 - Comment #6')
    )
),
(
    2,
    JSON_ARRAY(
        JSON_OBJECT('at', NOW(), 'content', 'Post #2 - Comment #1'),
        JSON_OBJECT('at', NOW(), 'content', 'Post #2 - Comment #2'),
        JSON_OBJECT('at', NOW(), 'content', 'Post #2 - Comment #3'),
        JSON_OBJECT('at', NOW(), 'content', 'Post #2 - Comment #4')
    )
);

Records: 2  Duplicates: 0  Warnings: 0


SELECT 
	JSON_SET(`comments`, '$."[*]".content', 'Lorem ipsum ...')
FROM `posts`


JSON_SET(`comments`, '$."[*]".content', 'Lorem ipsum ...')


[{"at": "2023-03-24 08:34:40.000000", "content": "Post #1 - Comment #1"}, {"at": "2023-03-24 08:34:40.000000", "content": "Post #1 - Comment #2"}, {"at": "2023-03-24 08:34:40.000000", "content": "Post #1 - Comment #3"}, {"at": "2023-03-24 08:34:40.000000", "content": "Post #1 - Comment #4"}, {"at": "2023-03-24 08:34:40.000000", "content": "Post #1 - Comment #5"}, {"at": "2023-03-24 08:34:40.000000", "content": "Post #1 - Comment #6"}]

[{"at": "2023-03-24 08:34:40.000000", "content": "Post #2 - Comment #1"}, {"at": "2023-03-24 08:34:40.000000", "content": "Post #2 - Comment #2"}, {"at": "2023-03-24 08:34:40.000000", "content": "Post #2 - Comment #3"}, {"at": "2023-03-24 08:34:40.000000", "content": "Post #2 - Comment #4"}]