Update statement takes lot of time . Need help in optimization.

Question

Hi,
I need to update values from table ARPU_2009_2010 to table TST_MICRO_SEG_PREP.
Table ARPU_2009_2010 contains around 400000 records. Table TST_MICRO_SEG_PREP contains 374000 customers. I need to update values for each customer in the table TST_MICRO_SEG_PREP.
Please find below query used:
UPDATE TST_MICRO_SEG_PREP a
SET
ARPU_2009_2010_REV=(select case when cnt>0 then round((sum(total_rev)/cnt),2) else 0 end arpu from ARPU_2009_2010 b
where a.subno=b.subno
group by subno,cnt)
This query takes more than 4 hours to execute. All tables used are having proper index.
Kindly suggest an alternative for this.
Thanks,
Kabilan
Edited by: 946887 on Jul 16, 2012 11:44 PM

Answer 1

>
UPDATE table1 X
SET
ARPU=(select case when cnt>0 then round((sum(total_rev)/cnt),2) else 0 end arpu from table2 Y
where X.subno=Y.subno
group by subno,cnt)
>
Are you intending to update all the 400K rows in table1 ? If not, then you have to rewrite the query.
>
This query takes more than 4 hours to execute.
>
Did you try to monitor what it's doing when the query is getting executed.
>
I tried to execute using stored procedures and sp also takes much time.
>
What makes you to think that stored procedure will execute more efficiently compared to a single DML statement ?
>
Kindly suggest an alternative for this.
>
As mentioned in the earlier post try to follow the guidelines. Only then it will be feasible to suggest some alternatives by looking at some metrics.
Thanks
Raj