I need help with a, b, c in Databases question.

10.21 Answer the following questions based on the company logical database sehema EMPLOYEE Fname | Minit Lname Bdate Address Sex SalarySupersan Dno DEPARTMENT Mgr san Mar start date DEPT LOCATIONS PROJECT Dnum WORKS ON Hours DEPENDENT ent came SexBdate Relationship (a) Explain primary key constraint, and show an example based on the company database schema (b) Explain entity integrity constraint, and show an example based on the company database schema (c) Explain referential integrity constraint, and show two examples based on the company database schema. Explain the following query in English (based on company database) SELECT FNAME, LNAME, SSN FROM EMPLOYEE WHERE NOT EXISTS (SELECT FROM WORKS ONB WHERE (B.PNO IN (SELECT PNUMBER FROM PROJECT WHERE DNUMBER-5) AND NOT EXISTS (SELECT FROM WORKS ON c WHERE C.ESSN-SSN AND C.PNO B.PNO) )Modity the query to list employees who work on any of the projects controlled by department number5