SQL断言语句

Question

Consider the following two Relational Schema describing the EMPLOYEES and DEPARTMENTS of some organization (assume all names are unique).

EMPLOYEES (EmployeeName, Salary, DeptName)

DEPARTMENTS (DeptName, ManagerName, City)

Define at schema level, a constraint (SQL Assertion) which specifies that none of the salaries of the employees of any department located in 'San Francisco' is more than the salary of any employee in the 'Management' department.

My approach:

create assertion CHECK_SALARY as CHECK
(   

not exists (select * from EMPLOYEES

where select salary from EMPLOYEES

where EMPLOYEES.DeptName = 'San Fransisco' <

select salary from EMPLOYEES

where EMPLOYEES.DeptName = 'Management'

)

this is the thing i wrote but it is not working properly, any suggestions are appreciated

Answer 1

Try something like this:

CREATE ASSERTION check_salary AS CHECK (   
  NO EXTISTS ( SELECT * FROM employees
               WHERE ( SELECT MAX(salary) FROM employees
                       WHERE "DeptName" = 'San Fransisco' )
                   < ( SELECT MIN(salary) FROM employees
                       WHERE "DeptName" = 'Management' ) )
);

Answer 2

尝试这个。

CREATE ASSERTION check_salary AS CHECK (NO EXTISTS ( SELECT * FROM Employees ee, departments dd WHERE  ee.dept_name = dd.dept_name AND dd.city = 'San Francisco' AND ee.salary < (SELECT Max(salary_amount) FROM Employees e, Departments d WHERE e.dept_name =d.dept_name AND d.Dept_name = 'Management') ));