سؤال داتابيس1 لغة sql -ddl

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Q1: Consider the following relational database:

(EMPLOYEE ( Person_Name, Street, City
(WORKS ( Person_Name, Company_Name, Salary
(COMPANY ( Company_Name, City
(MANAGES ( Person_Name, Manager_Name

1) Give an SQL DDL definition of these database
objects, use appropriate data types and include the following integrity constraints in the DDL definition:

 Identify and include referential integrity constraints that should hold in this database.
 All cities are mandatory fields and their default value is Riyadh and should be of the same data type.
 Salaries should range from 10,000 to 25,000 and the default value of the employee street address is ‘123M.St.’.
 Employees cannot be deleted if they are working for a company.

2) After defining these database objects apply and answer the following:
a)

Add a constraint called EmpMgr which ensure that there is no employee managed by manager lives in Riyadh.

b)

Remove the default value for the street address of the employee.

c)

Define a view called SalaryAvg consisting of manager name and the average salary of all employees who work for that manager.

d)

Why the database system should not allow updates to be expresses through
SalaryAvg view? Provide an example

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