SQL was designed as a set-oriented processing language. Some business rules( or poor physical design) require performing actions on row-by-row basis. Consider the following example:
. Increase the price of books <=$15 by 15%
. Decrease the price of books > $15 by 10%
Here is a set-oriented solution:

update titles set price = price *$1.15 where price < = $15
update titles set price = price *$0.9 where price > $15

Using Cursor:

Declare titles_curs cursor for
  select ytd_sales, price from titles for update of price
go
declare @total_sales int, @price money
open titles_curs
fetch next from titles_curs into @total_sales,@price
if (@@fetch_status = -1)
begin
  print ‘No books found’
  close titles_curs
  deallocate titles_curs
  return
end

while (@@fetch_status = 0)
begin
  if @total_sales = null
    update titles set price = @price * 0.75 where current of titles_curs
  else
    if @price >$15
      update titles set price = @price * 0.9 where current of titles_curs
    else
      update titles set price = @price * 1.15 where current of titles_curs
  fetch next from titles_curs into @total_sales, @price
end
if (@@fetch_status = -2)
  raiserror (‘Attempt to fetch deleted row’, 16,1)
close titles_curs
deallocate titles_curs

A major advantage of cursors is that you can avoid multiple passes of a table.
The advantage is performance; cursors introduce substantial overhead to a basic table scan.
Our recommendation : Use cursors to avoid many, many passes of the data. Seek alternative coding methods and compare for best performance, replace two update sentences to one:

update titles set price = price *
                                                               case
                                                                   when price < 20 then 1.1
                                                                   else 0.9 
                                                                end