Crystal Report Filtering Problem

[newbie26]

hey.can someone help me..???
how can i filter records from the database depending on
the length of each record???

example..i only want to display records with the length
of the fieldname lastname <> 5.

what is the formula for this using crystal report??
im currently using this:

length({tablename.fieldname}) <> 5
but this doesn't work when i use it with not like syntax.

length({tablename.fieldname}) <> 5 and not({tablename.fieldname} like 'a*')

i badly need this..thanks in advance.
im using vb6, mysql and crystal report 8.