Problem while creating a trigger for automatic generation of primary key values

Question

I'm trying to create a trigger for automatic generation of primary key values using sequences on Oracle SQL Developer.

Since I'm new to this, it sounds kind of vague to me so I tried various things I found online but failed to create what I am supposed to do. I tried this piece of code but I am completely sure that it is wrong.

CREATE OR REPLACE TRIGGER TRIGGER1
BEFORE INSERT ON Orders
FOR EACH ROW
    WHEN (new.ID IS NULL)
BEGIN
    :new.ID := Orders_SEQ.NEXTVAL;
END;

Can someone guide me to what am I supposed to do for this question?

Answer 1

I tried this piece of code but I am completely sure that it is wrong.

Why? It is completely correct.

SQL> create table orders (id number);

Table created.

SQL> create sequence orders_seq;

Sequence created.

SQL> CREATE OR REPLACE TRIGGER TRIGGER1
  2  BEFORE INSERT ON Orders
  3  FOR EACH ROW
  4      WHEN (new.ID IS NULL)
  5  BEGIN
  6      :new.ID := Orders_SEQ.NEXTVAL;
  7  END;
  8  /

Trigger created.

SQL> insert into orders (id) values (null);

1 row created.

SQL> select * from orders;

        ID
----------
         1

SQL>