7.3. Statement Level Aggregation
Statement triggers can enforce business rules where the rule is based on a table aggregate. Although a row trigger can restrain a salary for a particular row, a statement trigger can constrain the result of SUM(salary). This is essentially a constraint on the entire table.
This is quite different from constraints discussed so far. Initially, simple rules are enforced with a CHECK constraint. Chapter 6 illustrates a more complex rule that restricts the salary for any professor in the English department while leaving the CHECK constraint to enforce a salary restriction for non-English professors.
Consider the following rules.
A professor cannot be added if the current budget exceeds $55,000.
The total budget cannot ...
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