Access 2007[c] The Missing Manual

4. Blocking Bad Data

Even the best database designer has spent a sleepless night worrying about the errors that could be lurking in a database. Bad data's a notorious problemit enters the database, lies dormant for months, and appears only when you discover you've mailed an invoice to customer "Blank Blank" or sold a bag of peanuts for$4.99.

The best way to prevent these types of problems is to stop bad data from making it into your database in the first place. In other words, you need to set up validation rules that reject suspicious values as soon as someone types them in. Once bad data's entered your database, it's harder to spot than a blueberry in a swimming pool.

This chapter covers the essential set of Access data validation tools:

• The basics include duplicates, required fields, and default values.

• Input masks format ordinary text into patterns, like postal codes and phone numbers .

• Validation rules lay down strict laws for unruly fields.

• Lookups limit values to a list of preset choices.