$15$ a$)$ What is an assertion? How they differ from triggers?

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b$)$ Consider the following relation schema and write SQL queries to find:

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EMPLOYEE$($Fname$,$ Minit, Lname, SSN$,$ Bdate, Address, Sex, Salary SuperSSN, Dno$)$

DEPARTMENT$($Dname$,$ Dnumber, MgrSSN$,$ MgrStartDate$)$

DEPT$\_$LOCATIONS$($Dnumber$,$ Dlocaions$)$

PROJECT$($Pname$,$ Pnumber, Plocation,Dnum$)$

WORKS$\_$ON$($ESSN$,$ Pno,Hours$)$

i$.$ Retrieve the name and address of all employees who work for the 'Research' department.

ii$.$ For each employee, retrieve the employee's name, and the name of his or her immediate supervisor.

iii. Retrieve the name of each employee who works on all the projects controlled by department number $5.$

iv$.$ Make a list of all project numbers for projects that involve an employee whose last name is 'Smith' as a worker or as a manager of the department that controls the project.

v$.$ Retrieve the SSN of all employees who work on project number $1,2,$ or $3.$