query variables

hi,

i've a problem. i would like to use document object type as variable, is it possible?? this is my query

IF $[INV.ObjType] = '13'

SELECT T0.[Code], T0.[Name] FROM [dbo].[@XTIPODOC] T0 WHERE T0.[U_XTD_GRUPPO] = 'C'

i would like to change this IF $[INV.ObjType] = '13' in a variable, So as to create a single query for various documents.

thanks a lot