Selecting NOT EXISTS With Text Fields...?

 

I have three user tables (identical structure) that holds customer information. Each has about 1200 records, give or take a dozen, 99% of which are identical. However, there are a few records in each table that differ. Im trying to select the differences in these tables using a query.
Each customer has a custmer ID, but cust_id 1234 in table a may not be the same customer as cust_id 1234 in table b. Therefore, i am trying to compare using the cuLoginName field which is the username/email address text field. This is  what differentiates the records.

I have tried using


select cust_id, cuLoginName
from tblCustomerA
where NOT exists (
select cuLoginName from tblCustomerB)

to get the different records between the two tables (i.e. those in A but not in B), but even though there are two users in A that do not appear in B, the results are coming back with nothing. I am guessing this is a problem comparing on text fields?

What is an effective way around this problem?

Thanks