How can I force a database trigger to fire only if there is an update not when insert

Question

Hi
Could you help me please. I have a data base trigger that need
to fire only when there is an update in some columns in a table
But the trigger is firing eventhough they only do an insert.
here is the begining of the trigger.
create or replace trigger alpha_HZ_LOCATIONS_AUR
after update of address1,address2,city,state
,postal_code,county,province,country,attribute20
on hz_locations
for each row
DECLARE
v_cust_account_id hz_cust_acct_sites_all.cust_account_id%type;
v_cust_acct_site_id hz_cust_acct_sites_all.cust_acct_site_id%
type;
v_org_id hz_cust_acct_sites_all.org_id%type;
-- cursor; all sites for this customer address
cursor sc is
select
s.site_use_id site_use_id
,s.attribute15 frk_addr_number
from
ra_site_uses_all s
where s.address_id = v_cust_acct_site_id
and s.site_use_code in ('BILL_TO','SHIP_TO');
rowcnt number;
v_system_code varchar2(15);
v_ora_cust_num varchar2(30);
v_frk_cust_num varchar2(15);
v_insert_update_flag varchar2(1);
BEGIN
v_insert_update_flag := 'U';
-- get cust_acct_site_id (address_id)
begin
select acct_site.cust_account_id,
acct_site.cust_acct_site_id, acct_site.org_id
into v_cust_account_id, v_cust_acct_site_id, v_org_id
from
hz_party_sites party_site
,hz_cust_acct_sites_all acct_site
where acct_site.party_site_id = party_site.party_site_id
and party_site.location_id = :new.location_id;
Thank you much
alpha

Answer 1

Thanks for the response. My trigger is firing when I update the
table trough a form. Also when the uses go into the oracle apps
and create a new customer they get an error saying
ora-01403 no data found
ora-06512 at'the trigger name' and gives line number
ora-04088 error during execution of trigger.
Note: and I looked trigger it's really ok.
If you can please help