General Qualification
You can use the following constructions to form a where clause:
• not qual
• qual or qual
• qual and qual
• (qual)
where qual is a condition that qualifies a query. For example:
where e.age <= 50
where (e.age <=50) and (j.salary >= 40000) and
(e.job=j.jid)
These examples apply boolean operators to the results of each predicate. If boolean operators are not specified, the result of the qual condition is the result of the predicate. Not(true) is false, not(false) is true, not(unknown) is unknown. AND and OR are defined by the tables that follow.
The following table shows the results of the AND Logical Operator:
The following table shows the results of the OR Logical Operator: