How do I automatically reset a sequence's value to 0 every year in Oracle 10g?

Question

As in the question, how do I automatically reset an Oracle sequence\'s value back to 0 every year in Oracle 10g?

I\'m using the sequence to generate an identifier i

Answer 1

I have found that was best to create a trigger and a table. The table will contain the year and sequence for the year. The trigger gets the current year, verifies the table, if none registry found, then inserts a new one starting from 1. Otherwise, select the last and increments by one, updating the corresponding table.

The Table:

create table GDRDOCUMENTOSEQ
(
  noano NUMBER(4),
  noseq NUMBER(6)
)
;
alter table GDRDOCUMENTOSEQ
  add unique (NOANO);

The Trigger:

CREATE OR REPLACE TRIGGER "GDRGUIARESSARCIMENTONODOC_BIR"
BEFORE INSERT ON GDR.GDRGUIARESSARCIMENTO
FOR EACH ROW

DECLARE
  lNoAno number;
  lNoSeq number;
  lQtd   number;
begin

  SELECT EXTRACT(YEAR FROM SYSDATE) into lNoAno FROM DUAL;

  SELECT COUNT(0)
    INTO lQtd
    FROM gdr.gdrdocumentoseq ds
   WHERE ds.noano = lNoAno;

  IF lQtd = 0 then
    lNoSeq := 1;
    INSERT INTO GDR.GDRDOCUMENTOSEQ (NOANO, NOSEQ) VALUES (lNoAno, lNoSeq);
  else
    SELECT nvl(max(ds.noseq), 0) + 1
      INTO lNoSeq
      FROM gdr.gdrdocumentoseq ds
     WHERE ds.noano = lNoAno;

    UPDATE GDR.GDRDOCUMENTOSEQ ds
       SET ds.noseq = lNoSeq
     WHERE ds.noano = lNoAno;
  end if;

  :new.nodocumento := SUBSTR(lNoAno, 3) || lpad(lNoSeq, 6, '0');

end;

I have this code running in production from 2016. Currenty state of the table is:

NOANO   NOSEQ   
2017    1411    
2016    237