Retreiving specific content in a Database table field

[Airwe Josh]

I require a solution:
I have a large database storing among many things GPS codes. The codes are in 7 digits. However users have been entering less or more than seven digits worse still some have entered letters and spaces. I need a query that can pull only such erroneous records for editing. Using length() function i have been able to deal with the less or more than 7 digits however i am no seeking a solution for checking whether letter have been entered.

Thanks in advance