php script to update mysql field within a loop

I need to write a script in php
which updates single field in mysql table

count itemcode where itemcode is equalto "abcdef"
first i have to count no of times one single value appears in the itemcode

use it for a loop

for(icnt=0, icnt<count, icnt=icnt+1)
{
update itemcode // fieldname
where itemcode="abcdef" // field with value abcdef
with 'ip'+icnt // to be replaced with a contstant 'ip" plus counter
}


I am not too good with programming
but can someone please help me with it....

i need to do this on a running project