create table myjsontable 
( 
    id number, 
    json_data clob constraint is_json CHECK (json_data IS JSON ) 
)

insert into myjsontable (id,json_data) values (1,'{"emp_name": "Yazhini", "emp_dob":"10/10/1995" }')

insert into myjsontable (id,json_data) values (2,'{"emp_name": "Hema", "emp_dob":"10/10/1992" }')

select * from myjsontable

Accessing data from JSON column

select id,mj.json_data.emp_name,mj.json_data.emp_dob from myjsontable mj

Lets create table with out JSON constraint present

create table myjsontable_nocons   
(   
    id number,   
    json_data varchar2(1000)  
)

When there is no constraint available, we cannot access the JSON attributes directly and it fails

select id,mj.json_data.emp_name,mj.json_data.emp_dob from myjsontable_nocons mj

insert into myjsontable_nocons (id,json_data) values (2,'{"emp_name": "Hema", "emp_dob":"10/10/1992" }')

insert into myjsontable_nocons (id,json_data) values (1,'{"emp_name": "Yazhini", "emp_dob":"10/10/1995" }')

use Treat as JSON statement in combination with "WITH" statement to access JSON data that is stored in regular CLOB or NVARCHAR columns.

with result  as    
(    
   select id, TREAT(json_data as JSON) json_data  
     from myjsontable_nocons    
)    
select id, r.json_data.emp_name, r.json_data.emp_dob  
from result r