Help for Pl/SQL Logic & Syntax used

Question

Hi, in Ivan Bayross' book, following example is given illustrating use of triggers.
Create trigger audit_trail
After update or delete on customer
for each row
DECLARE
oper VARCHAR(20);
BEGIN
If updating then
oper :='UPDATE';
End if;
If deleting then
oper :='DELETE';
End if;
Insert into audit_cust
Values(*:OLD.CUST_NO* , *:OLD.FNAME* );
END;
Questions :*
1. Why : symbol is used in insert query above? Viz. :OLD.CUST_NO
what does it indicate ?? ALso, what does . ( dot operator) indicates?
OLD is not table name.
2. In the program above what does this line mean??
If deleting then
oper :='DELETE';
End if;
We are just assigning value 'DELETE' to oper variable ?? or something else??

Answer 1

Hi,
So, still struggling on Ivan's book, eh ;-) ?
1. :OLD and :NEW means you can refer to the old and new column values.
They are only usable in triggers.
So, if you're updating column X from 1 to 2, the value of :OLD.X = 1 and :NEW.X = 2 in your trigger only.
http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/triggers.htm#CNCPT118
http://www.oracle.com/pls/db102/search?word=TRIGGER&partno=
We are just assigning value 'DELETE' to oper variable ?? or something else??I guess the autor meant do do this:
Create trigger audit_trail
After update or delete on customer
for each row
DECLARE
oper VARCHAR(20);
BEGIN
If updating then
oper :='UPDATE';
End if;
If deleting then
oper :='DELETE';
End if;
Insert into audit_cust
Values( :OLD.CUST_NO, : OLD.FNAME,  oper );
END;He probably forgot to insert the oper variable in his audit table,