I need help with this database question

10.21 Answer the following questions based on the company logical database sehema EMPLOYEE Fname Minit Lname Bdate Address SexSa Super ssnDno DEPARTMENT Mgr san Mar start date DEPT LOCATIONS PROJECT WORKS ON ena Hours DEPENDENT name Sex Bdate Relationship (a) Explain primary key constraint, and show an example based on the company database (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 ON B 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) Modify the query to list employees who work on any of the projects controlled by department number5 e)