Cursor locking the table - sql

Question

declare
CURSOR C1
IS select tgt.exp_date ,(src.eff_date - 1/(24*60*60))eff_date
from mira_rate tgt,mira_rate_dummy src
where src.tc_code = tgt.tc_code and src.carrier_code = tgt.carrier_code and tgt.exp_date is null for update of tgt.exp_date;
v_a date;
v_b date;
i number:=0;
begin
open c1;
loop
fetch c1 into v_a, v_b;
exit when c1%notfound;
update mira_rate
set exp_date =v_b where current of c1;
i:=i+1;
end loop;
dbms_output.put_line(i||' rows updated');
close c1;
commit;
end;
After i excecute the query it is locking the table says
ORA-00054: resource busy and acquire with NOWAIT specified
Also pls tell me how to remove the lock i tried killing the sesssion it is not happening.still it says the same
Affter removing the lock. Pls clear me this requirement
select tgt.exp_date ,(src.eff_date - 1/(24*60*60))eff_date
from mira_rate tgt,mira_rate_dummy src
where src.tc_code = tgt.tc_code and src.carrier_code = tgt.carrier_code and tgt.exp_date is null;
it ill return rows I need to goto the mira_rate table need to update exp_date=eff_date.
Please suggest me how to do i m using Oracle 9i so merge without not matched is working

Answer 1

At first sight, there is no commit in the code.
The code with commit wil be ok. Commit will release the locks(Oracle cursor examples/expl)
But better you would:
MERGE INTO mira_rate tgt
USING mira_rate_dummy src
ON (src.tc_code = tgt.tc_code and src.carrier_code = tgt.carrier_code)
WHEN MATCHED THEN UPDATE
SET exp_date= src.eff_date - 1/(24*60*60) --or just src.eff_date
WHERE tgt.exp_date is null;
This is what you want to do as far as I understand.
As a rule: What you can do in SQL, do in SQL, not PL/SQL.

Answer 2

Take out the 'FOR UPDATE'.
You need to be very clear in your mind why you need it and in my experience you generally don't.
Between us I think we are saying this should be your approach
begin
UPDATE mira_rate
SET exp_date= src.eff_date - 1/(24*60*60)
WHERE exp_date is null;
DBMS_OUTPUT.PUT_LINE
(TO_CHAR(SQL%ROWCOUNT) || ' Rows Updated);
end;
No need for locks and no need for cursors.
Hope that helps.
Edit - still not entirely sure what your requirement is but the following sql may be what you are looking for.
UPDATE MIRA_RATE TGT
SET EXP_DATE =
(
SELECT SRC.EFF_DATE - 1/86400
FROM MIRA_RATE_DUMMY SRC
WHERE
SRC.TC_CODE = TGT.TC_CODE AND
SRC.CARRIER_CODE = TGT.CARRIER_CODE
)
WHERE
TGT.EXP_DATE IS NULL;

Answer 3

#Satheesh, Updatable select will work only for primary key columns. See if the select fetches the primary key and also useins it in where clause. Else the update will throw error.
There is something to check for
cannot modify a column which maps to a non key-preserved table
You can have join but the update needs primary key to update in the base table.