Simple IBM DB2 Trigger - triggers

Question

I'm trying to create a trigger in DB2 (AS400) to insert/delete a row into a table when an insert/delete is triggered on a different table, but I need to use information about the triger table.
The example would be I would like is like this (column 1 from table 1 and table 2 are the same and unique in table 2):
CREATE TRIGGER MY_TRIGGER
AFTER INSERT OR DELETE ON DB1.TABLE1
BEGIN
IF INSERTING
THEN INSERT INTO DB1.TABLE2 (Col1, Col2) VALUES (Db1.TABLE1.Col1, 0);
ELSEIF DELETING
THEN DELETE FROM Db1.TABLE2 WHERE Col1=TABLE1.Col1;
END IF;
END
But this doesn't work (it doesn't recognize TABLE1.Col1 on insert/delete statements).
Also it would prompt me an error (I guess) since it would create a duplicate key when a second row is inserted in Table 1. How could I avoid errors (just skip the insert) when the Table2.Col1 already exists?

Answer 1

Try adding correlation names like this:
CREATE TRIGGER MY_TRIGGER
AFTER INSERT OR DELETE ON DB1.TABLE1
REFERENCING OLD ROW AS OLD
NEW ROW AS NEW
BEGIN
IF INSERTING
THEN INSERT INTO DB1.TABLE2 (Col1, Col2) VALUES (NEW.Col1, 0);
ELSEIF DELETING
THEN DELETE FROM Db1.TABLE2 WHERE Col1=OLD.Col1;
END IF;
END
The trigger has access to both the old and new image of a row. You need to tell it which to use. BTW, only the update action populates both the old and new image. Insert only provides the new image, and delete only provides the old image. One might think that SQL could figure that out, but no, you still have to tell it explicitly.
EDIT This is the final trigger actually used (from comments, thank you #MarçalTorroella)
CREATE TRIGGER MY_TRIGGER
AFTER INSERT OR DELETE ON DB1.TABLE1
REFERENCING OLD ROW AS OLD
NEW ROW AS NEW
FOR EACH ROW MODE DB2ROW
BEGIN
DECLARE rowcnt INTEGER;
IF INSERTING THEN
SELECT COUNT(*)
INTO rowcnt
FROM DB1.TABL2
WHERE Col1 = NEW.Col1;
IF rowcnt = 0 THEN
INSERT INTO DB1.TABLE2 (Col1, Col2)
VALUES (NEW.Col1, 0);
END IF;
ELSEIF DELETING THEN
DELETE FROM Db1.TABLE2
WHERE Col1=OLD.Col1;
END IF;
END