Data quality problems in database

Due to the lack of following mechanisms, DBA generally do mistakes to maintain data quality:

1. Use of NULL- e.g. a customer's  contact number is null. It is very difficult to know whether the customer has no contact number or has never been asked to give their contact number.
   
   
2. Referential  Integrity:  e.g.  an orders inventory with an order allocated to customer number C0010, where that customer does not appear within the customer inventory.
   
   
3. Value checking for reasonableness: e.g.   customer's date of birth is 12/12/1850.
   
   
4. Values constrained to a pre-defined domain – e.g.  a user is adding record can add a customer title of ‘test' instead of selecting from a list of pre-defined values like Mr, Mrs, Dr etc.