Access 2007 for Starters: The Missing Manual

Chapter 4. Blocking Bad Data

• Data Integrity Basics

• Input Masks

• Validation Rules

• Lookups

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 problem—it 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 basicsinclude duplicates, required fields, and default values.

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

• Validation ruleslay down strict laws for unruly fields.

• Lookupslimit values to a list of preset choices.

Data Integrity Basics

All of Access's data validation features work via the Design view you learned about in Chapter 2. To put them in place, you choose a field and then tweak its properties. The only trick's knowing what properties are most useful. You've already seen some in Chapter 2, but the following sections fill in a few more details.

Tip

Remember, Access gives you three ways to switch to Design view. You can right-click ...