Chapter 29. 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 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 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.

Data Integrity Basics

All of Access’s data validation features work via the Design view you learned about in Chapter 27. 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 27, but the following sections fill in a few more details.


Remember, Access gives you three ways to switch to Design view. You can right-click the table tab title and then choose Design View from the ...

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