Write relational algebra queries for the two specifications below using the relations also defined below:
a. retrieve the names of customers who have ordered parts costing less than $150.00.
b. retrieve the names of customers and the partname of orders with a qty greater than 10.
parts(pno, pname, qoh, price, olevel)
customers(cno, cname, street, zip, phone)
employees(eno, ename, zip, hdate)
zip_codes(zip, city, state)
orders(ono, cno, eno, received, shipped)
odetails(ono, pno, qty)
where qoh stands for quantity on hand and olevel stands for (re)order level. the p, c, e and o single letter prefixes for attributes refer to the parts, customers, employees and orders relations, respectively. the other attribute names are self-explanatory.