The Condition Box

1. When it is difficult or impossible to express all constraints on the domain variables within the skeleton tables, the condition box may be used.
2. To add the constraint that we are only interested in customers other than Jones to the above query, we include the condition box:

   

3. To find all account numbers with balances between $1,300 and $1,500:

   

   

4. Logical expressions and and or may appear in the condition box.
5. To find all account numbers where the balance is between $1,300 and $2,000, but is not $1,500:

   

   

6. An unconventional use of the or construct allows comparison with several constant values: