Wrong use of bind variable in WHEN of a trigger - sql

Question

I'm fairly new in SQL and I'm trying to set up a TRIGGER for an exercise I have. I can't seem to find the solution. Here is the code:
CREATE TRIGGER C3
BEFORE UPDATE OF rate ON Magazines
FOR EACH ROW
WHEN(:NEW.rate < :OLD.rate*0.75)
BEGIN
IF :NEW.rate < 0 THEN
:NEW.rate = 0;
RAISE_APPLICATION_ERROR(-20003, 'Rate should never be below 0.');
ELSE
:NEW.rate = :OLD.rate*0.75;
END;
/
When I try to compile, it shows me this error :
Non valid use of bind variable in WHEN of a trigger
I tried to remove the : before NEW and OLD but instead it gives me another compiler error.
Any ideas?
Thanks a lot!

Answer 1

The assignment operation in pl/sql is :=
CREATE TRIGGER C3
BEFORE UPDATE OF rate ON Magazines
FOR EACH ROW
WHEN(:NEW.rate < :OLD.rate*0.75)
BEGIN
IF :NEW.rate < 0 THEN
:NEW.rate := 0;
RAISE_APPLICATION_ERROR(-20003, 'Rate should never be below 0.');
ELSE
:NEW.rate := :OLD.rate*0.75;
END;

Answer 2

You first need to remove the colons from the WHEN clause only. Then you will also need colons in front of the equals signs for assignment in the trigger body.
CREATE TRIGGER C3
BEFORE UPDATE OF rate ON Magazines
FOR EACH ROW
WHEN(NEW.rate < OLD.rate*0.75)
BEGIN
IF :NEW.rate < 0 THEN
:NEW.rate := 0;
RAISE_APPLICATION_ERROR(-20003, 'Rate should never be below 0.');
ELSE
:NEW.rate := :OLD.rate*0.75;
END;
/
Per the documentation:
In the trigger_body of a simple trigger or the tps_body of a compound trigger, a correlation name is a placeholder for a bind variable. Reference the field of a pseudorecord with this syntax:
:pseudorecord_name.field_name
In the WHEN clause of a conditional trigger, a correlation name is not a placeholder for a bind variable. Therefore, omit the colon in the preceding syntax.