G-3150: Try to use identity columns for surrogate keys.
Minor
Maintainability, Reliability
Restriction
ORACLE 12c
Reason
An identity column is a surrogate key by design – there is no reason why we should not take advantage of this natural implementation when the keys are generated on database level. Using identity column (and therefore assigning sequences as default values on columns) has a huge performance advantage over a trigger solution.
Example (bad)
CREATE TABLE locations (
location_id NUMBER(10) NOT NULL
,location_name VARCHAR2(60 CHAR) NOT NULL
,city VARCHAR2(30 CHAR) NOT NULL
,CONSTRAINT locations_pk PRIMARY KEY (location_id)
)
/
CREATE SEQUENCE location_seq START WITH 1 CACHE 20
/
CREATE OR REPLACE TRIGGER location_br_i
BEFORE INSERT ON LOCATIONS
FOR EACH ROW
BEGIN
:new.location_id := location_seq.nextval;
END;
/
Example (good)
CREATE TABLE locations (
location_id NUMBER(10) GENERATED ALWAYS AS IDENTITY
,location_name VARCHAR2(60 CHAR) NOT NULL
,city VARCHAR2(30 CHAR) NOT NULL
,CONSTRAINT locations_pk PRIMARY KEY (location_id))
/