Update ID if Sequence MAX_VALUE reached - oracle

Question

I am using the following TRIGGER to Insert in my TEST Table:
create or replace
TRIGGER TRG_CYCLE
BEFORE INSERT ON TEST_CYCLE
FOR EACH ROW
BEGIN
IF :NEW.LOGID IS NULL
THEN SELECT SEQ_CYCLE.nextval INTO :NEW.LOGID from dual;
END IF;
END;
SEQ_CYCLE is the Sequence. Now I have to use the CYCLE option in order to start with 1 after the MAX_VALUE is reached. Since I don't want duplicate LOGIDs I want to do an UPDATE if the LOGID exists, if not an INSERT. Can I do this inside the Trigger?

Answer 1

If I understand well, you may need an INSTEAD OF trigger; to build such a trigger you need to create a VIEW over your table and build the trigger on this view.
For example, say you have:
create sequence SEQ_CYCLE maxValue 3 cycle nocache;
create table TEST_CYCLE ( logId number, someColumn varchar2(20));
You can create a view and a trigger over the view:
create or replace view v_test_cycle as select * from test_cycle;
create or replace trigger trgCycle
instead of insert on v_test_cycle
for each row
declare
vCheck number;
vSeqVal number := SEQ_CYCLE.nextVal;
begin
select count(*)
into vCheck
from v_test_cycle
where logId = vSeqVal;
--
if vCheck = 0 then
insert into test_cycle(logId, someColumn) values ( vSeqVal, :NEW.someColumn);
else
update test_cycle
set someColumn = :NEW.someColumn
where logId = vSeqVal;
end if;
end;
If you do the INSERTs on the view, this is what you get:
SQL> select * from test_cycle;
no rows selected
SQL> insert into v_test_cycle(someColumn) values('some value 1');
1 row created.
SQL> insert into v_test_cycle(someColumn) values('some value 2');
1 row created.
SQL> insert into v_test_cycle(someColumn) values('some value 3');
1 row created.
SQL> insert into v_test_cycle(someColumn) values('some value 4');
1 row created.
SQL> insert into v_test_cycle(someColumn) values('some value 5');
1 row created.
SQL> select * from test_cycle;
LOGID SOMECOLUMN
---------- --------------------
1 some value 4
2 some value 5
3 some value 3
SQL>