GENERATED BY DEFAULT AS IDENTITY

Question

Hi,
How to use GENERATED BY DEFAULT AS IDENTITY in oracle.
thank you

Answer 1

Actually, there is no way to mimic GENERATED BY DEFAULT AS IDENTITYin Oracle 100%. GENERATED BY DEFAULT AS IDENTITY means generate unique value if value is not provided. You can get as close as:
SQL> create table tbl(id number,val varchar2(10))
  2  /
Table created.
SQL> create sequence tbl_seq
  2  /
Sequence created.
SQL> create or replace
  2    trigger tbl_bir
  3    before insert
  4    on tbl
  5    for each row
  6    begin
  7        :new.id := nvl(:new.id,tbl_seq.nextval);
  8  end;
  9  /
Trigger created.
SQL> insert into tbl(val) values('ABC')
  2  /
1 row created.
SQL> insert into tbl values(-1,'DEF')
  2  /
1 row created.
SQL> select * from tbl
  2  /
        ID VAL
         1 ABC
        -1 DEF
SQL> -- OK so far, however look what happens if we want to issign NULL to id:
SQL>
SQL> insert into tbl values(null,'XYZ')
  2  /
1 row created.
SQL> select * from tbl
  2  /
        ID VAL
         1 ABC
        -1 DEF
         3 XYZ
SQL> SY.