Rules and Triggers

Hi:

Are there cases when triggers are faster than rules?
It appears that on the database that I used; rules
used sequential scan while triggers used index scan.
I had a table "sc_redeem". There is a rule which I
place on that table. The body of rule is "
CREATE RULE rule_update_redeem as
ON insert TO sc_redeem
DO
UPDATE sc_customer_card
SET redeemed = redeemed + new.points,
balance = balance - new.points
WHERE customer_id = new.customer_id AND
card_type_cd = new.card_type_cd;"

The index of sc_customer_card is on the field
"customer_id". I noticed when I use the SQL statement.
EXPLAIN INSERT INTO sc_redeem(....) VALUES (....);
It reported that it performed a sequential scan on the
table sc_customer_card (around 100,000+ records w/
unique customer id for each record).

I tried converting the rule to function & trigger
and it reported that it used an Index scan given the
same INSERT statement.

I was wondering why the rule used sequentail scan
and the equivalent function trigger used index scan.

Thank you,
ludwig lim

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