Autonumbering for a primary key

How do you create a column with auto-numbering that can be used as a primary key? This is a very simple and probably very common problem. Here is a simple and universal procedure to do this.

1. Create a column in the table with the number datatype; this will be used to hold the auto-generated numbers.

2. Create a sequence that will keep track of the auto number value.

3. Create a trigger that will insert the next value of your auto number into the newly created column every time the new insert occurs.

4. Replace schima_name, sequence_name, trigger_name, table_name, column_name, with appropriate values, like this: 

CREATE SEQUENCE schima_name.sequence_name 
INCREMENT BY 1 NOMAXVALUE MINVALUE 1 NOCYCLE CACHE 20 NOORDER; 

CREATE OR REPLACE TRIGGER schima_name.trigger_name 
BEFORE INSERT ON schima_name.table_name 
REFERENCING OLD AS OLD NEW AS NEW 
FOR EACH ROW 
BEGIN 
  SELECT sequence_name.NEXTVAL 
     INTO :NEW.column_name 
  FROM DUAL; 
END;

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This was first published in January 2002

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