Re: [HACKERS] update by one transaction

> I have a table for instance boci (row_number int, col2 float, col3
> float). The boci table has about 10000 rows. 
> I want to update col3 column of the table in every row with different
> values. Desired values are in an array has 10000 elements. I want to be
> the value of the col3 column in the first row equal to the first element
> of the array and so on. 
> I've done it with a 'for' cycle, but it is very slow. I want to do
> theese updates with one transaction. 
> 
> Here is a little piece of my program:
> 
> PQexec(conn, "BEGIN");
> for (i=0; i<10000; i++)
> {
>     sprintf(buff, "UPDATE boci SET col3 = %f WHERE row_number=%d",
> array[i], i);
>     PQexec(conn, buff);
> }
> PQexec(conn, "END");
> 
> I can't solve this problem with COPY command becouse I have to update
> col3 column in every minute, but I don't want to change row_number and
> col2 columns. My problem is the updating and not the creation of the
> table. Creation is fast enough.
> This program is very, very slow. Is there any way making this program
> much faster (for instance with CURSOR or 'block write' or something
> else)? Please write me a little program that describes your ideas!

Try creating an index on row_number. Right now to do the update the whole
table has to be scanned. With an index only the matching rows will be
scanned. 

-dg

David Gould           dg@illustra.com            510.628.3783 or 510.305.9468
Informix Software                      300 Lakeside Drive   Oakland, CA 94612
 - A child of five could understand this!  Fetch me a child of five.