demo.sql

drop table if exists t;
create table t (data json(object));
declare
   x varchar2(40 byte) := '{ "greet": "merry x-mas" , "to": "all" }';
begin
   insert into t values (x);
end;
/
declare
   x varchar2(20 byte) := '{xmas:[1,2,3,4,5,6]}';
begin
   insert into t values (x);
end;
/

select length(data) from t;