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Access 2013 For Dummies by Ken Cook, Laurie Ulrich Fuller

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Chapter 15

Express Yourself with Formulas

In This Chapter

arrow Developing an expression

arrow Performing complex calculations

arrow Calculating text fields

arrow Using the Expression Builder

Efficient database design requires that tables contain only necessary fields. Too many fields can cause a table to load slowly — you won’t notice the difference with a few hundred records, but you certainly will with a few hundred thousand. So what fields are often added unnecessarily to a table’s design? The short answer: fields that could be generated from calculations on data stored in other fields.

For example, suppose you have a Products table with a UnitPrice field and an OrderDetails table with a Quantity field. You may be tempted to add an Amount field to your OrderDetails table that stores the result of multiplying UnitPrice times Quantity. This is unnecessary because Access can perform these calculations on the fly — in what’s called a calculated field.

A calculated field takes information from another field or fields in the database and performs some arithmetic to come up with new information. Access calls ...

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