MySQL 8.0

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SELECT @@version


@@version


8.0.36


CREATE TABLE `tab` ( `jsdata` VARCHAR(1000) )
INSERT INTO `tab` VALUES
('{"x": 1, "y": 2, "z": 3}'),
('{"e": 4, "k": 5}')

Records: 2  Duplicates: 0  Warnings: 0


WITH k AS
(
SELECT *, 
       ROW_NUMBER() OVER(PARTITION BY `jsdata` ORDER BY value DESC) AS rn,
       JSON_KEYS(`jsdata`) AS jk
  FROM `tab` AS t
  JOIN JSON_TABLE(
                 `jsdata`,
                '$.*' COLUMNS (value INT PATH '$')
       ) j
)
SELECT JSON_UNQUOTE(JSON_EXTRACT(jk, CONCAT('$[',rn-1,']'))) AS "key", value
  FROM k


key
value


e
5

k
4

x
3

y
2

z
1


SELECT JSON_UNQUOTE(
       JSON_EXTRACT(JSON_KEYS(`jsdata`), 
                    CONCAT('$[',
                    ROW_NUMBER() OVER(PARTITION BY `jsdata` ORDER BY value DESC)-1,
                    ']'))) AS "key", value
  FROM `tab` AS t
  JOIN JSON_TABLE(
                 `jsdata`,
                '$.*' COLUMNS (value INT PATH '$')
       ) j


key
value


65
5

6b
4

78
3

79
2

7a
1