CREATE TABLE job ( 
    jobid               NUMBER(28) NOT NULL, 
    jobname             VARCHAR2(100) NOT NULL 
) 
LOGGING

CREATE UNIQUE INDEX job__idxv2 ON 
    job ( 
        jobname 
    ASC ) 
        LOGGING

ALTER TABLE job ADD CONSTRAINT job_pk PRIMARY KEY ( jobid )

ALTER TABLE job ADD CONSTRAINT job__un UNIQUE ( jobname )

CREATE SEQUENCE job_jobid_seq START WITH 1 NOCACHE ORDER

CREATE OR REPLACE TRIGGER job_jobid_trg BEFORE 
    INSERT ON job 
    FOR EACH ROW 
    WHEN ( new.jobid IS NULL ) 
BEGIN 
    :new.jobid := job_jobid_seq.nextval; 
END; 

INSERT INTO job (jobName) VALUES ('M100')

INSERT INTO job (jobName) VALUES ('M100')

INSERT INTO job (jobName) VALUES ('m100')

INSERT INTO job (jobName) VALUES ('m100')

select * from job