Rails - Nov 2005 - Passing variables with update_all

I''d like to produce an SQL update along the lines of:
UPDATE companies SET category2={newcategory} WHERE (category2 = 
{oldcategory})

At the moment I''ve got:

ctype = params[:ctype]
Company.update_all("category2=ctype", "category2=ctype")

At present this returns a StatementInvalid:
Unknown column ''ctype'' in ''where clause'':
UPDATE companies SET
category2=ctype WHERE (category2 = ctype)

Can anyone tell me how I can pass the variable successfully?

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