Using if statement in a trigger to prevent autoincrement for a restore

Question

I use the following trigger to simulate an autoincrement on the primary key id, each time a row is inserted:
CREATE OR REPLACE TRIGGER "ITPLAN".BI_VORHABEN BEFORE INSERT ON VORHABEN REFERENCING NEW AS NEW FOR EACH ROW
DECLARE
     nKey NUMBER;
BEGIN
SELECT seq_vorhaben.NEXTVAL INTO nKey FROM dual;
:NEW.ID := nKey;
END;
now for a restore procedure, I want to keep the id of all rows, that are restored from an archive table. this trigger however will increment the value with each insert. Therefor I want to insert a condition that applies the trigger only if the ID value is null:
if (vorhaben.id is null) then :NEW.ID := nKey
unfortunately I get a compilation error. thanks for any help.

Answer 1

How about ...
CREATE OR REPLACE TRIGGER "ITPLAN".BI_VORHABEN
BEFORE INSERT ON VORHABEN
REFERENCING NEW AS NEW
FOR EACH ROW
WHEN (new.id IS NULL)
DECLARE
nKey NUMBER;
BEGIN
SELECT seq_vorhaben.NEXTVAL INTO nKey FROM dual;
:NEW.ID := nKey;
END;
/Actually, I'm not sure that the variable is needed, is it? Can you just do ...
CREATE OR REPLACE TRIGGER "ITPLAN".BI_VORHABEN
BEFORE INSERT ON VORHABEN
REFERENCING NEW AS NEW
FOR EACH ROW
WHEN (new.id IS NULL)
BEGIN
SELECT seq_vorhaben.NEXTVAL INTO :NEW.ID FROM dual;
END;
/