Adding information into one field that depends what is in another

Hi,

Im kind of stuck how to do this, i just tried using "when" and "then" commands in sql and its wiped my data.

My table is called "customer_info" and i have a field called "retailer". Retailer is dependant on a field called "clas".

Basically i would like to insert "4" into retailer where clas is equal to "glass".
And then reuse this command to do several more statements that are pretty much the same but just the values are changing.

Thanks in advance!Ha, i managed to sort it with a simple update query! No help needed now.

Cheers