Postgres 15

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select version();

version

PostgreSQL 15.0 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-10), 64-bit

SELECT 1

create table my_table(id   integer  generated always as identity
                                     primary key 
                     , data jsonb
                     ); 
                     
insert into my_table(data) values ('{}'), ('{"notes": "Inserted"}');  

select * from my_table;
select data::jsonb ? 'notes' from my_table where id in (1,2);

CREATE TABLE

INSERT 0 2

id
data

1
{}

2
{"notes": "Inserted"}

SELECT 2

?column?

f

t

SELECT 2

update my_table 
   set data = case when data::jsonb ? 'notes' 
                   then jsonb_set(data::jsonb, array['notes'], (data->'notes')::jsonb || '["Update"]'::jsonb)
                   else jsonb_set(coalesce(data::jsonb,'{}'), '{notes}', '["Add"]'::jsonb)
              end   
 where id in (1,2); 

UPDATE 2

select * from my_table;
select data::jsonb ? 'notes' from my_table where id in (1,2);

id
data

1
{"notes": ["Add"]}

2
{"notes": ["Inserted", "Update"]}

SELECT 2

?column?

t

t

SELECT 2