I have a query which is the record source for a form, this query references an unbound text box txtFieldID.
SELECT tblTrials.FLD_ID AS FieldID, tblTrials.PRNUM AS prnum, IIf([prnum] Like "A*",Mid([PRNUM],2,5),IIf([prnum] Like "b*",Mid([PRNUM],2,5),[prnum])) AS prnum_num
FROM tblTrials
WHERE...