adding case statment with SELECT

I had asked how to get the LEFT JOIN to work with the following statement and got a great response.  However, now I'm stuck on another issue.    s.class and s.nir are numeric identifiers that do not have an associated table as a reference.   Can I add a case statement within the select to show their textual value?

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SELECT   s.batch, s.code, s.class as Package_Type, s.nir as NIR_type, s.account, s.arrival, s.return, f.name as Feed_Type, s.describe, s.due, b.item as Special_Item, b.amount as Special_Amt, ;
             s.farmname, c.first, c.last, c.business, c.discount, c.pricetier, s.postage, c.billto, c.address1, c.city, c.state, c.zip, ;
             c.fax, c.phone, c.email;  
   FROM samples s ;
  INNER JOIN samplexp x ON s.sampleid = x.sampleid ;
  INNER JOIN clients c ON s.account = c.account ;
  INNER JOIN feedcode f ON s.feed_type = f.feed_type ;
  LEFT JOIN billitem b ON s.sampleid = b.sampleid ;
  WHERE s.batch = 11748 ;
    AND x.location="LANCSAMPLE"
 
COPY TO C:\lancasterTest\lancBill TYPE DELIMITED

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