This procedure performs the same changes to the underlying table as the procedure written without a cursor, but it uses cursors instead of set-oriented programming. As each row is fetched, examined, and updated, a lock is held on the appropriate data page. Also, as the comments indicate, each update commits as it is made, since there is no explicit transaction.
/* Same as previous example, this time using a
** cursor. Each update commits as it is made.
*/
create procedure increase_price_cursor
as
declare @price money
/* declare a cursor for the select from titles */
declare curs cursor for
select price
from titles
for update of price
/* open the cursor */
open curs
/* fetch the first row */
fetch curs into @price
/* now loop, processing all the rows
** @@sqlstatus = 0 means successful fetch
** @@sqlstatus = 1 means error on previous fetch
** @@sqlstatus = 2 means end of result set reached
*/
while (@@sqlstatus != 2)
begin
/* check for errors */
if (@@sqlstatus = 1)
begin
print "Error in increase_price"
return
end
/* next adjust the price according to the
** criteria
*/
if @price > $60
select @price = @price * 1.05
else
if @price > $30 and @price <= $60
select @price = @price * 1.10
else
if @price <= $30
select @price = @price * 1.20
/* now, update the row */
update titles
set price = @price
where current of curs
/* fetch the next row */
fetch curs into @price
end
/* close the cursor and return */
close curs
return
Which procedure do you think will have better performance, one that performs three table scans or one that performs a single scan via a cursor?
