How can i create auto increment column to my existing column? - oracle12c

Question

I am working with Oracle 12c in which I have below table structure:-
CREATE TABLE patients (
patient_id Integer NOT NULL,
customer_id Integer NOT NULL,
title varchar(5) NOT NULL,
fname varchar(125) NOT NULL,
lname varchar(125) NOT NULL,
dob date NOT NULL,
is_medical_card NUMBER(1) NOT NULL CHECK (is_medical_card IN (0,1)),
scheme_number Integer NOT NULL,
status varchar(50) NOT NULL,
created_on date NOT NULL,
last_update_date date NOT NULL,
consent_flag NUMBER(1) NOT NULL CHECK (consent_flag IN (0,1)),
relationship varchar(50) NOT NULL
);
Where patient_id is my primary key so now I want to make it auto increment as well so please let me how can I do this so make it auto increment.
Thanks!
Need to create auto increment to existing column.

Answer 1

You might want to use Identities - Creating a table with an Identity gives you the chance to omit the ID values and let Oracle use a sequence on your desired column:
1. Let's Create the Table:
CREATE TABLE identities (
id NUMBER GENERATED BY DEFAULT ON NULL AS IDENTITY,
description varchar2(100) NOT NULL
);
Table created.
2. You'll want to create a primary key to ensure uniqueness:
alter table identities add constraint id_pk primary key (ID);
Table altered.
3. Let's insert some data in different ways:
INSERT INTO identities (description)
VALUES('Insert Description omitting ID');
1 row created.
INSERT INTO identities (id,description)
VALUES(NULL,'Insert with explicit NULL value');
1 row created.
4. Save the work done
commit;
Commit complete.
5. Check the results
select * from identities;
ID DESCRIPTION
---------- ---------------------------------------------
1 Insert Description omitting ID
2 Insert with explicit NULL value
As you can see we dind't specify any number for the ID, but the Identity on the ID column did for us
Note: Mind that you can manually insert an ID, but this will mess up with the Identity as it'll normally do with a standard Sequence:
INSERT INTO identities (id,description)
VALUES(3,'Manually insert an ID value');
1 row created.
INSERT INTO identities (description)
VALUES('Test Nextval');
INSERT INTO identities (description)
*
ERROR at line 1:
ORA-00001: unique constraint (XXX.ID_PK) violated
This error, because it tries to insert a '3' into the ID that was manually inserted with the statement before.
Check the table:
select * from identities;
ID DESCRIPTION
---------- ---------------------------------------------
1 Insert Description omitting ID
2 Insert with explicit NULL value
3 Manually insert an ID value
Re-Run the "NEXTVAL" insert:
INSERT INTO identities (description)
VALUES('Test Nextval');
1 row created.
Re-Check the table:
select * from identities;
ID DESCRIPTION
---------- ---------------------------------------------
1 Insert Description omitting ID
2 Insert with explicit NULL value
3 Manually insert an ID value
4 Test Nextval
Hope this Helps.