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);

SELECT * FROM contact;

Records: 3  Duplicates: 0  Warnings: 0




name_field
address_field
contact_age


Mary
address one
25

Fred
address two
35

Bill
address three
47


SELECT JSON_ARRAYAGG(JSON_OBJECT('name_field', name_field,
                                 'address_field', address_field,
                                 'contact_age', contact_age)) all_contacts
FROM contact;


all_contacts


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


SELECT CONCAT('[',
         GROUP_CONCAT(
           CONCAT(
               '{',
               CONCAT_WS(', ', 
                   '"name_field:"', JSON_QUOTE(name_field), 
                   '"address_field:"', JSON_QUOTE(address_field), 
                   '"age_field:"', contact_age
                   ),
               '}'
              )
            ),
         ']'    
         ) one_value
FROM contact


one_value


[{"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}]