ORACLE中建立自增字段的方法

今天有人问起，写在这里，便于以后CP
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1. 建立 SEQUENCE

    CREATE [ OR REPLACE ] SEQUENCE sequence_identity
    START WITH initial seed
     INCREMENT BY step
     MAXVALUE upper bound [NOMAXVALUE]
    NOCYCLE [empty]

2. 建立 TRIGGER

    CREATE [ OR REPLACE ] TRIGGER trigger_identity
    BEFORE INSERT ON table_name
    FOR EACH ROW
    BEGIN
        SELECT sequence_identity.NEXTVAL INTO :new.column_name FROM DUAL;
    END;