Trigger on Views in PL/SQL - sql

Question

I want to write a trigger in PL/SQL. My first aim is to compare two time_stamp data type (A and B). If one of these is bigger than another, for instance A>B, i will update columns on another table. Trigger that i try to write is like below.
CREATE OR REPLACE TRIGGER trigger_name
AFTER INSERT OR UPDATE OR DELETE ON views
FOR EACH ROW
DECLARE
A views.X%TYPE;
B views.Y%TYPE;
C views.Z%TYPE;
BEGIN
SELECT X, Y, Z INTO A, B, C FROM views;
IF A>B THEN
update another_table set D=' ' and E='UNRESOLVED' where column1=A;
ELSE
dbms_output.put_line('ABC: ' || A || ' < ' || 'CDE' || B);
END IF;
END;
If i execute this trigger, i'm getting error like below.
Error report:
ORA-25001: kan inte skapa den här triggertypen i den här typen av vy
25001. 00000 - "cannot create this trigger type on views"
*Cause: Only INSTEAD OF triggers can be created on a view.
*Action: Change the trigger type to INSTEAD OF.
Thanks in advance for your help.

Answer 1

You're nearly there. This is only a syntactic confusion. You cannot create a trigger that fires BEFORE or AFTER an insert or update or delete of a view, but you can create a trigger that fires INSTEAD OF an insert or update or delete:
TABLE BEFORE / AFTER insert or update or delete
VIEW INSTEAD OF insert or update or delete
And, as #Belayer writes, you don't (and shouldn't) use SELECT, use the automatically prepared record called :new for the new values during insert or update, or the record ':old' for the old values during update or delete.
Your trigger would look something like:
CREATE OR REPLACE TRIGGER views_tr
INSTEAD OF INSERT OR UPDATE OR DELETE ON views
FOR EACH ROW
BEGIN
IF :new.x > :new.y THEN
UPDATE another_table SET D=' ', ... WHERE column1 = :new.x;
ELSE
dbms_output.put_line('ABC: ' || :new.x || ' < ' || 'CDE' || :new.y);
END IF;
END views_tr;
/