MariaDB 10.4

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CREATE TABLE test (val JSON);
INSERT INTO test VALUES ('{
"key1": "value-1", 
"key2": "value-2",
"key3": "value-3",
"key5": "value-5",
"key7": "value-7",
"key8": "value-8",
"key9": "value-9",
"key10": "value-10"
}');
SELECT * FROM test;


val


7b0a226b657931223a202276616c75652d31222c200a226b657932223a202276616c75652d32222c0a226b657933223a202276616c75652d33222c0a226b657935223a202276616c75652d35222c0a226b657937223a202276616c75652d37222c0a226b657938223a202276616c75652d38222c0a226b657939223a202276616c75652d39222c0a226b65793130223a202276616c75652d3130220a7d


SET @from := 3;
SET @till := 9;
WITH RECURSIVE cte AS ( SELECT @from num
                        UNION ALL
                        SELECT num+1 FROM cte WHERE num < @till )
SELECT CONCAT('key', num) `key`, 
       JSON_EXTRACT(test.val, CONCAT('$.key', num)) `value`
FROM test
CROSS JOIN cte
HAVING `value` IS NOT NULL;


key
value


key3
"value-3"

key5
"value-5"

key7
"value-7"

key8
"value-8"

key9
"value-9"

key	value
key3	"value-3"
key5	"value-5"
key7	"value-7"
key8	"value-8"
key9	"value-9"