which are horizontally fragmented on the department number, deptNo. Assume there is an integrity constraint that requires that every member of staff earns less than every manager in the same department. Further assume that we wish to insert the tuple (‘S9100’, ‘John Smith’, ‘1-May-1960’, 30000, ‘D1’) into the Staff relation. Under what conditions can this constraint be checked locally?

Question

Consider the following two relations:
```
Staff (staffNo, name, DOB, salary, deptNo)
Department (deptNo, deptName, managerStaffNo)
```

Answer 1

If a record has previously been inserted that satisfies the constraint, then that can be used as a basis
for a local integrity check. For example, suppose that department D1 already has an employee
S1000 whose salary is £40,000. Given that the constraint has not been violated by the existing
tuple, we know that the salary of every manager in department D1 is more than £40,000.
Therefore, it would be OK to insert a record with salary £30,000.