MySQL 8.0

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create table location (id int, name varchar(10), neighbors json);
insert into location (id, name) values
(1, 'loc1'), (2, 'loc2'), (3, 'loc3'), (4, 'loc4'), (5, 'loc5');

create table nearby (place int, nextdoor int, distance varchar(10), mygroup varchar(10));
insert into nearby values
(1, 2, '500m', 'g1'), (1, 3, '900m', 'g1'),
(2, 1, '500m', 'g3'), (2, 3, '100m', 'g4'), (2, 4, '80m', 'g4');
with flatten_neighbor as (
	select nn.place, nn.name, l.name as nextdoorname, nn.distance, nn.mygroup
	from (
		select l.id, l.name, n.place, n.nextdoor, n.distance, n.mygroup
		from location l
		join nearby n on n.place = l.id
	) nn
	join location l on l.id = nn.nextdoor
),
obj_by_place as (
	select *, json_object('name', nextdoorname, 'distance', distance) as jo from flatten_neighbor
),
concat_obj as (
	select place, mygroup, concat('[', group_concat(jo), ']') as jason from obj_by_place group by place, mygroup
),
final as (
	select place, json_objectagg(mygroup, jason) stuff from concat_obj group by place
)
select * from final;


place
stuff


1
{"g1": "[{"name": "loc2", "distance": "500m"},{"name": "loc3", "distance": "900m"}]"}

2
{"g3": "[{"name": "loc1", "distance": "500m"}]", "g4": "[{"name": "loc3", "distance": "100m"},{"name": "loc4", "distance": "80m"}]"}


with flatten_neighbor as (
	select nn.place, nn.name, l.name as nextdoorname, nn.distance, nn.mygroup
	from (
		select l.id, l.name, n.place, n.nextdoor, n.distance, n.mygroup
		from location l
		join nearby n on n.place = l.id
	) nn
	join location l on l.id = nn.nextdoor
),
obj_by_place as (
	select *, json_object('name', nextdoorname, 'distance', distance) as jo from flatten_neighbor
),
concat_obj as (
	select place, mygroup, concat('[', group_concat(jo), ']') as jason from obj_by_place group by place, mygroup
),
final as (
	select place, json_objectagg(mygroup, jason) stuff from concat_obj group by place
)
update location l join final f on l.id = f.place set l.neighbors = f.stuff;

select * from location;


id
name
neighbors


1
loc1
{"g1": "[{"name": "loc2", "distance": "500m"},{"name": "loc3", "distance": "900m"}]"}

2
loc2
{"g3": "[{"name": "loc1", "distance": "500m"}]", "g4": "[{"name": "loc3", "distance": "100m"},{"name": "loc4", "distance": "80m"}]"}

3
loc3
null

4
loc4
null

5
loc5
null


select * from location where json_extract(neighbors, '$.g3');


id
name
neighbors


2
loc2
{"g3": "[{"name": "loc1", "distance": "500m"}]", "g4": "[{"name": "loc3", "distance": "100m"},{"name": "loc4", "distance": "80m"}]"}

place	stuff
1	{"g1": "[{"name": "loc2", "distance": "500m"},{"name": "loc3", "distance": "900m"}]"}
2	{"g3": "[{"name": "loc1", "distance": "500m"}]", "g4": "[{"name": "loc3", "distance": "100m"},{"name": "loc4", "distance": "80m"}]"}

id	name	neighbors
1	loc1	{"g1": "[{"name": "loc2", "distance": "500m"},{"name": "loc3", "distance": "900m"}]"}
2	loc2	{"g3": "[{"name": "loc1", "distance": "500m"}]", "g4": "[{"name": "loc3", "distance": "100m"},{"name": "loc4", "distance": "80m"}]"}
3	loc3	null
4	loc4	null
5	loc5	null