Query within the Cursor loop is very slow

Question

Hi ,
I have a stored procedure which has Select/Insert operation which is looped within the cursor. The Select uses variables from the cursor, and inserts the data into the table.
My problem is the peformance. The stored procedure executes in 2 mins if I hard code the where clause values in the Select. Instead if I use the variables obtained from the cursor, the query takes so long (more than 20 mins) to insert the same no of records into the table.
Below is the snippet of my code
create procedure sample is
declare
v_acct_month number(2);
v_sp_name varchar2(30);
cursor v_cur is Select distinct Acct_Month,salesperson_name from period;
begin
open v_cur;
loop
fetch v_cur into v_acct_month, v_sp_name;
exit when v_cur%notfound;
Insert into T1
Select * from T2,T3.. Where T2.month=v_acct_month,t3.sp_name=v_sp_name;
end loop;
End;
The query is not using the optimizer when the variables are used.The optimizer is used when I hard code the values in the select.
Please give me suggestions to make this query faster..
Thanks,
Arun
Edited by: [email protected] on Mar 28, 2009 10:18 AM

Answer 1

Hi,
Whenever you write code, format it to show the scope of BEGIN, LOOP, IF statements, and so on.
Type these 6 characters
{code}
(small letters only, inside curly brackets) before and after the formatted code, to preserve spacing on this site.
You've discovered why the tecnique you're using is called "slow-by-slow" processing.
You don't need a cursor. You may not even need PL/SQL.
Just write an INSERT statement that reference the table from the cursor and the tables from your current INSERT statement.
Here's one way:
INSERT
INTO     t1 (columns)
SELECT         columns
FROM     t2
,     t3
WHERE     ...
AND     (t2.month, t3.sp_name)     IN (
                          SELECT DISTINCT
                               acct_month
                       ,        salesperson_name
                       FROM        period
                       );Depending on the details of your case, there may be a better way, such as a 3-way join.