????...Can You Explain with some data...
You should try using the LEFT() function. For example, if I had the values ['Monkey', 'Mother', 'Morph', 'Freddy', 'Norway'] stored in a field, I could do:
IF LEFT([field], 2) = 'Mo' THEN 'Match' ELSE 'No Match' END
I could then use the output of that formula to filter my results to only show all the matches (in this case, all the entries which begin with 'Mo').
If you're in need of more robust matching, check out the REGEX matching function. You can specify a dynamic array of text to match using the REGEX functions.
Hope that helps,