Extract key from JSON string in MySQL - mysql

Question

My table contains string in json format. I need to get the sum and average of each key.
+----+------------------------------------------------------------------------------------+------------+
| id | json_data | subject_id |
+----+------------------------------------------------------------------------------------+------------+
| 1 | {"id": "a", "value": "30"}, {"id": "b", "value": "20"}, {"id": "c", "value": "30"} | 1 |
+----+------------------------------------------------------------------------------------+------------+
| 2 | {"id": "a", "value": "40"}, {"id": "b", "value": "50"}, {"id": "c", "value": "60"} | 1 |
+----+------------------------------------------------------------------------------------+------------+
| 3 | {"id": "a", "value": "20"} | 1 |
+----+------------------------------------------------------------------------------------+------------+
Expected result is
{"id": "a", "sum": 90, "avg": 30},
{"id": "b", "sum": 70, "avg": 35},
{"id": "c", "sum": 120, "avg": 40}
I've tried
SELECT (
JSON_OBJECT('id', id, 'sum', sum_data, 'avg', avg_data)
) FROM (
SELECT
JSON_EXTRACT(json_data, "$.id") as id,
SUM(JSON_EXTRACT(json_data, "$.sum_data")) as sum_data,
AVG(JSON_EXTRACT(json_data, "$.avg_data")) as avg_data
FROM Details
GROUP BY JSON_EXTRACT(json_data, "$.id")
) as t
But no luck. How can I sort this out?

Answer 1

Input json needs to correct
create table json_sum (id int primary key auto_increment, json_data json);
insert into json_sum values (0,'[{"id": "a", "value": "30"}, {"id": "b", "value": "20"}, {"id": "c", "value": "30"}]');
insert into json_sum values (0,'[{"id": "a", "value": "40"}, {"id": "b", "value": "50"}, {"id": "c", "value": "60"}]');
insert into json_sum values (0,'[{"id": "a", "value": "20"}]');
select
json_object("id", jt.id, "sum", sum(jt.value), "avg", avg(jt.value))
from json_sum, json_table(json_data, "$[*]" columns (
row_id for ordinality,
id varchar(10) path "$.id",
value varchar(10) path "$.value")
) as jt
group by jt.id
Output:
json_object("id", jt.id, "sum", sum(jt.value), "avg", avg(jt.value))
{"id": "a", "avg": 30.0, "sum": 90.0}
{"id": "b", "avg": 35.0, "sum": 70.0}
{"id": "c", "avg": 45.0, "sum": 90.0}