Blocking Bad Data
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This article will explain how to set up validation rules in your Access 2007 database that will save you lots of headaches. It is excerpted from chapter four of
Access 2007: The Missing Manual, written by Matthew MacDonald (O'Reilly, 2006; ISBN: 0596527608). Copyright © 2006 O'Reilly Media, Inc. All rights reserved. Used with permission from the publisher. Available from booksellers or direct from O'Reilly Media.
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 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 the table tab title and then choose Design View from the menu, use the Home -> View button on the ribbon, or use the tiny view buttons at the Access window’s bottom-right corner. And if you’re really impatient, then you don’t even need to open your table first—just find it in the navigation pane, right-click it there, and then choose Design View.
Next: Preventing Blank Fields >>
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 This article is excerpted from chapter four of Access 2007: The Missing Manual, written by Matthew MacDonald (O'Reilly, 2006; ISBN: 0596527608). Check it out today at your favorite bookstore. Buy this book now.
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