THE RELATIONAL MODEL 1: INTRODUCTION, QBE, AND RELATIONAL ALGEBRA - Concepts of Database Management - page 40

This example requires you to search for a range of values to find all customers with balances between
$1,000 and $5,000. When you ask this kind of question, you are looking for all balances that are greater than
$1,000 and all balances that are less than $5,000; the answer to this question requires using a compound cri-
terion, or two criteria in the same field.
To place two criteria in the same field, separate the criteria with the AND operator to create an AND
condition. Figure 2-13 shows the AND condition to select all records with a value of more than 1000 and less
than 5000 in the Balance field.

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Two conditions
for a single field

FIGURE 2-13 Query that uses an AND condition for a single field

The query results appear in Figure 2-14.

Only cutomers with
balances between $1,000
and $5,000 are included

FIGURE 2-14 Query results

COMPUTED FIELDS

Sometimes you'll need to include calculated fields that are not in the database in queries. A computed field
or calculated field is a field that is the result of a calculation using one or more existing fields. Example 7 illus-
trates the use of a calculated field.