MySQL 8.0

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CREATE TABLE contact
(
     name_field VARCHAR  (5) NOT NULL,
  address_field VARCHAR (20) NOT NULL,
  contact_age   INTEGER      NOT NULL
);

INSERT INTO contact
VALUES
('Mary', 'address one',   25),
('Fred', 'address two',   35),
('Bill', 'address three', 47);



Records: 3  Duplicates: 0  Warnings: 0


SELECT
CONCAT
('[', REPLACE
  (
    REPLACE
    (
      GROUP_CONCAT
      (
        JSON_ARRAY
        (
          'name_field:', name_field, 
          'address_field:', address_field, 
          'age_field:', contact_age
        ) SEPARATOR ','
      ), '[', '{'
    ), ']', '}'
  ), ']'
) 
AS best_result2 
FROM contact

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SEPARATOR ','
      ), '[', '{'
    ), ']', '}'
  ), ']'
) 
AS best_result2 
FRO' at line 14


SELECT
CONCAT
('[', REPLACE
  (
    REPLACE
    (
      GROUP_CONCAT(
        JSON_ARRAY
        (
          'name_field:', name_field, 
          'address_field:', address_field, 
          'age_field:', contact_age
        ) SEPARATOR ','
      ), '[', '{'
    ), ']', '}'
  ), ']'
) 
AS best_result2 
FROM contact


best_result2


[{"name_field:", "Mary", "address_field:", "address one", "age_field:", 25},{"name_field:", "Fred", "address_field:", "address two", "age_field:", 35},{"name_field:", "Bill", "address_field:", "address three", "age_field:", 47}]