1. When it is diffcult 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, weinclude the condition box:
| conditions |
| _xï¿¢ = Jones |
3. To find all account numbers with balances between $1,300 and $1,500:
| deposit | bname | account# | cname | balance |
| P. | _x |
| conditions |
|
_x≥1300 _x1500
|
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:
| deposit | bname | account# | cname | balance |
| P. | _x |
| conditions |
|
x = (≥1300 and ≤2000 and ï¿¢1500) |
6. An unconventional use of the or construct allows comparison with several constant values:
| conditions |
| _x = (Burnaby or Richmond) |