MySQL 5.7

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CREATE TABLE articolo( data JSON );
INSERT INTO articolo VALUES
(
'{
    "produttori": [
        "8",
        "9"
    ],
    "articoli_alternativi": [
        "3",
        "9"
    ],
    "articoli_accessori": [
        "5",
        "6",
        "7",
        "8"
    ],
    "tecnologie": [],
    "fornitori": [
        "9",
        "8"
    ],
    "classificazioni": [
        "3",
        "4"
    ]
}'
)
SELECT data 
  FROM articolo 
 WHERE JSON_CONTAINS(JSON_EXTRACT(data, "$.fornitori"), "2", "$")


data


SELECT data
  FROM 
  (
    SELECT  @i := @i + 1 AS rn,
            JSON_UNQUOTE(JSON_EXTRACT(data,CONCAT('$.fornitori[',@i-1,']'))) AS elm,
           data               
      FROM information_schema.tables 
     CROSS JOIN articolo 
     CROSS JOIN (SELECT @i := 0) r
  ) q
 WHERE elm = 8
     


data


7b22666f726e69746f7269223a205b2239222c202238225d2c202270726f647574746f7269223a205b2238222c202239225d2c20227465636e6f6c6f676965223a205b5d2c2022636c61737369666963617a696f6e69223a205b2233222c202234225d2c202261727469636f6c695f6163636573736f7269223a205b2235222c202236222c202237222c202238225d2c202261727469636f6c695f616c7465726e6174697669223a205b2233222c202239225d7d