MySQL 8.0

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CREATE TABLE `test` (`test` JSON);

INSERT INTO `test` VALUES
    (JSON_ARRAY(JSON_OBJECT('a', '1', 'b', '2'),
                JSON_OBJECT('a', '1', 'b', '-2'),
                JSON_OBJECT('a', '2', 'b', '3'),
                JSON_OBJECT('a', '2', 'b', '-3'),
                JSON_OBJECT('a', '3', 'b', '4'))),
    (JSON_ARRAY()),
    (JSON_ARRAY());
    
SELECT CAST(test AS CHAR) FROM test;


CAST(test AS CHAR)


[{"a": "1", "b": "2"}, {"a": "1", "b": "-2"}, {"a": "2", "b": "3"}, {"a": "2", "b": "-3"}, {"a": "3", "b": "4"}]

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WITH 
cte1 AS (
    SELECT *, ROW_NUMBER() OVER () rn
    FROM test 
    ),
cte2 AS (
    SELECT cte1.*, jsontable.a, jsontable.b
    FROM cte1
    CROSS JOIN JSON_TABLE(cte1.test, 
                          '$[*]' COLUMNS ( a VARCHAR(255) PATH '$.a',
                                           b VARCHAR(255) PATH '$.b')) jsontable
    WHERE jsontable.a <> 1
    ),
cte3 AS (    
    SELECT test, rn, JSON_ARRAYAGG(JSON_OBJECT('a', a, 'b', b)) new_test
    FROM cte2
    GROUP BY test, rn
    )
UPDATE test
JOIN cte3 ON test.test = cte3.test
SET test.test = cte3.new_test;
SELECT CAST(test AS CHAR) FROM test;


CAST(test AS CHAR)


[{"a": "2", "b": "3"}, {"a": "2", "b": "-3"}, {"a": "3", "b": "4"}]

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