Inserting checkbox values into one field

I have a checkboxes on my page (.aspx) like

checkbox1 - item1

checkbox2 - item2

checkbox3 - item3

etc

what i want is that when a user selects certain checkboxes

they should be inserted into a table called

customer which has fields (customer id and actions)

the data should be inserted as

customerid actions

1 item1,item2,item3

2 item1,item3

3 etc..

i.e all the values should be inserted into database into one field separated by commas.

Thanks