Question

I want to insert new values to an Oracle table. The table is quite large and the ID codes are stored as numbers. I’d like to write insert statements that can add my new information and assign an ID automatically which isn’t already taken.

For example:

insert into example_table values
(
(select max(person_id)+1 from example_table),
99, 'example name', 'example type');

But this code above obviously wouldn’t work, because I am specifying an ID (99). If I set 99 to null in the above code snippet, will it then work? Not sure how to format.

Thanks.

Answer 1

you can do this by defining a sequence and trigger on the database table.
The sequence will simply vend id’s in sequential order. The trigger will fire when the row is inserted and ask the sequence for the next available id , which it will then put into the table for you.. This way, passing NULL will work ok..

CREATE SEQUENCE YOUR_SCHEMA_NAME.IDSEQ
  START WITH 9988
  MAXVALUE 999999999999999999999999999
  MINVALUE 1
  NOCYCLE
  NOCACHE
  NOORDER;

CREATE OR REPLACE TRIGGER YOUR_SCHEMA_NAME.YOUR_TABLE_NAME_bir
BEFORE INSERT
ON YOUR_SCHEMA_NAME.YOUR_TABLE_NAME REFERENCING NEW AS NEW
FOR EACH ROW

BEGIN

  -- Custom code to: generate primary key from idseq if no id is passed

  IF :NEW.id IS NULL THEN
    :NEW.id := idseq.NEXTVAL;
  END IF;

EXCEPTION
  WHEN OTHERS THEN
    raise_application_error(-20570, 'System error: ' || SQLCODE || ':' || SQLERRM, TRUE);
END;
/