hi all, i m trying to get records matching a number in a comma separated values in a field

i have a table in which products details are stored and a field stored ID's of categories in which that product should be listed,

for example a product is to be listed in 5 categories having ID's 1,5,8,15,88. so if i want to match a product that should go in category with id 8

how can i do that... it must match a product having value 8 not 18, 88 or so...