Postgres 14

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create table if not exists customer (
    _id serial,
    first_name varchar(50),
    constraint pk_customer primary key (_id)
);
insert into customer(first_name) values ('Customer1');
1 rows affected

insert into customer(first_name) values ('Customer2');
1 rows affected

SELECT json_build_object('Customer',json_agg(customer)) as customer FROM customer;


customer


{"Customer" : [{"_id":1,"first_name":"Customer1"}, 
 {"_id":2,"first_name":"Customer2"}]}