Postgres 13

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE mytable
    ("id" int, "value" varchar(6))
;
    
INSERT INTO mytable
    ("id", "value")
VALUES
    (1, 'value1'),
    (2, 'value2'),
    (3, 'value3'),
    (4, 'value4'),
    (5, 'value5'),
    (6, 'value6');
    
SELECT * FROM mytable
6 rows affected



id
value


1
value1

2
value2

3
value3

4
value4

5
value5

6
value6


ALTER TABLE mytable
ALTER COLUMN "value" TYPE json USING json_build_object('t1', 'val', 'value', "value");
SELECT * FROM mytable


id
value


1
{"t1" : "val", "value" : "value1"}

2
{"t1" : "val", "value" : "value2"}

3
{"t1" : "val", "value" : "value3"}

4
{"t1" : "val", "value" : "value4"}

5
{"t1" : "val", "value" : "value5"}

6
{"t1" : "val", "value" : "value6"}

id	value
1	{"t1" : "val", "value" : "value1"}
2	{"t1" : "val", "value" : "value2"}
3	{"t1" : "val", "value" : "value3"}
4	{"t1" : "val", "value" : "value4"}
5	{"t1" : "val", "value" : "value5"}
6	{"t1" : "val", "value" : "value6"}