MariaDB 10.2

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DROP TABLE IF EXISTS `myTable`;
CREATE TABLE IF NOT EXISTS `myTable` (
  `id` SERIAL,
  `config` TEXT
);
INSERT INTO `myTable`
  (`id`, `config`)
VALUES
  (126, '{"person": {"name": "", "details": {"age": 20}}}'),
  (127, '{"person": {"name": "zeca 2"}}');
UPDATE `myTable`
  SET `config` = JSON_SET(`config`, '$.person.name', 'zeca 1'),
      `config` = IF(JSON_EXISTS(`config`, '$.person.details') IS NOT NULL,
        JSON_SET(
          `config`,
          '$.person.details',
          JSON_OBJECT('age', 40)
        ),
        JSON_INSERT(
          `config`,
          '$.person',
          JSON_OBJECT('details',
            JSON_OBJECT('age', 40)
          )
        )
      )
WHERE `id` = 126;
UPDATE `myTable`
  SET `config` = JSON_SET(`config`, '$.person.name', 'zeca'),
      `config` = IF(JSON_EXISTS(`config`, '$.person.details') IS NOT NULL,
        JSON_SET(
          `config`,
          '$.person.details',
          JSON_OBJECT('age', 87)
        ),
        JSON_INSERT(
          `config`,
          '$.person',
          JSON_OBJECT('details',
            JSON_OBJECT('age', 87)
          )
        )
      )
WHERE `id` = 127;
SELECT `id`, `config`
FROM `myTable`;


id
config


126
{"person": {"name": "zeca 1", "details": {"age": 40}}}

127
{"person": {"name": "zeca", "details": {"age": 87}}}

id	config
126	{"person": {"name": "zeca 1", "details": {"age": 40}}}
127	{"person": {"name": "zeca", "details": {"age": 87}}}