Specify relational expressions for the following descriptions on the database schema shown in Figure 3.5 using the relational operators discussed in this chapter. Also show the result of each query if applied to the database of Figure 3.6.

(9) Retrieve the names of employees who do not work on any project.

Note: James Borg in working on a project even though the work hour is null.

(10) For each department, retrieve the department name, and the average salary of employees working in that department.

Tip: Grouping

EMPLOYEE FNAME MINIT LNAME SSN SEX SALARYSUPERSSN DNO Smith 123456789 1965-01-09 333445555 1955-12-08 999887777 1968-07-19 Wallace 9876543211941-06-20 Narayan666884444 1962-09-15 453453453 1972-07-31 987987987 1969-03-29 888665555 1937-11-10 638 Voss, Houston, TX 975 Fire Oak, Humble, TXM 5631 Rice, Houston, TX 980 Dallas, Houston, TX 450 Stone, Houston, TX Jabbar E Borg DEPT LOCATIONS DEPARTMENT DNAME DNUMBER MGRSSN MGRSTARTDATE 1995-01-01 1981-06-19 Headquarters WORKS_ON ESSN PNO HOURS PROJECT PNAME PNUMBER PLOCATION DNUM Bellaire 5 and 3 20 987654321 DEPENDENT ESSN DEPENDENT NAME SEX RELATIONSHIP 1983-10-25 F 195805-03 1942-02-28 1988-01-04 1988-12-30 1967-05-05 123456789 DAUGHTER SPOUSE