$2.$ Given the following schema.

Suppliers$($sID$,$ sName, address$)$

Parts$($pID$,$ pName, colour$)$

Catalog$($sID$,$ pID, price$)$

a$.$ Find the name and price of all blue parts. $[1$m$]$

b$.$ Find the name and price of all blue or red parts. $[2$m$]$

c$.$ Find all supplier names and addresses. $[1$m$]$

d$.$ Find the names of all suppliers that supply green parts. $[2$m$]$

e$.$ Find the name of parts that are blue and black. $[1$m$]$ Hint: Read the wording carefully.

f$.$ Find the total price of all parts. $[1$m$]$

g$.$ Find the average price of all parts based on colour. $[2$m$]$

$3.$ Given the following schema.

Student$($studentID$,$ studentName, studentAddress, phone$)$

Course$($courseID courseName, duration$)$

Enroll$($studentID$,$ courseID, semester, comments$)$

a$.$ Find the names of all students enrolled in semester $2.[1$m$]$

b$.$ List all course names and duration. $[1$m$]$

c$.$ List all courses with a duration less than $3.[1$m$]$

d$.$ List all student names who are enrolled in 'Database'. $[3$m$]$

e$.$ Discuss the differences between natural join, outer$-$join and theta$-$join. $[3$m$]$