Lab 1: An Algebraic Query Language
Lê Hồng Bảo Ngân – DE150159 – SE1502
I. We have the database schema consists of five relations:
Movies (title, year, length, genre, studioName, producer#)
StarsIn (movieTitle, movieYear, starName)
MovieStar (name, address, gender, birthdate)
MovieExec (producer#, name, address, netWorth)
Studio (name, address, presC#)
Write expressions of relational algebra to answer the following queries.
1. Find title and length of movies produced by Disney in 1990.
πtitle, length (σ(StudioName = “Disney”) and (year = 1990) (Movies))
2. Find date of birth of Aishwarya Rai who is a movie star.
πbirthday(σname = “Aishwararya Rai” (MovieStar))
3. Find the address of studio Film City.
π address (σname = “Film City” (Studio))
4. List name of the female stars in the film “Monsoon Wedding”.
πname(σ(gender = female) and (movieTitle = “Monsoon Wedding”) (MovieStar ⋈ StarsIn))
5. List name and gender of stars that appeared in movies produced by Sony in 2005.
π name, gender (σ(studioName = “Sony”) and (year = 2005) (MovieStar ⋈ Movies ⋈ StarsIn ))
6. Find name of the producer of Star Wars.
π producer# (σtitle = “Star Wars” (MovieExec ⋈ Movies))
7. Find name of executives that are worth more than Subhash Ghai.
a = πnetWorth(σname = “Subhash Ghai” (MovieExec))
πname(σnetWorth > a (MovieExec))
8. Find title of movies that are no longer than “Bride and Prejudice”.
a = πlength(σtitle = “Bridge and Prejudice” (Movies))
πname(σlength ≤ a (Movies))
9. List all the titles and years of movies that appeared in either the Movies or StarsIn
relation.
π title, year (Movies) U πmovieTitle, movieYear (StarsIn)
10. Find name and address of all male movie stars who are also movie executives with
a net worth under $10,000,000.
πname, address(σgender = male (MovieStar)) ⋂ πname, address (σnetWorth < $10,000,000
(MovieExec))
II. How to express constraints. via Relation Algebra
Give a schema:
PRODUCT (Maker, model)
PC (Model, Speed, RAM, HDD, Price)
LAPTOP (Model, Speed, RAM, HDD, Screen, Price)
PRINTER (Model, Color, Type, Price)
Use Relational Algebra to express following constraints:.9ol;
1. A black & white printer must be laser type
σcolor = false (σtype ≠ laser (Printer)) = ф
2. If a laptop has a larger (or equal) RAM and HDD than a PC, then the laptop must
also have a higher price than the PC
σ(Laptop.RAM ≥ PC.RAM) and (Laptop.HDD ≥ PC.HDD) (σLaptop.price ≤ PC.price (Laptop x PC)) = ф
3. No manufacturer of PC’s or Laptop’s may also make printers
(πmaker (Laptop) U πmaker (PC)) ⋂ πmaker (Printer) = ф
4. With the same Speed, a PC must have higher RAM and HDD than a Laptop
σPC.speed = Laptop.speed (Laptop x PC) ⋂ σ(PC.RAM ≤ Laptop.RAM) and (PC.HDD ≤ Laptop.HDD)
(Laptop x PC) = ф
5. With all computer (PC and Laptop), higher Speed, higher Price.
(πmodel(σPC1.speed > PC2.speed (σPC1.price ≤ PC2.price(PPC1(model, speed, RAM, HDD, price) (PC) ⋈
PPC2(model, speed, RAM, HDD, price) (PC) )))) U
(πmodel(σLaptop1.speed > Laptop2.speed (σLaptop1.price ≤ Laptop2.price(PLaptop1(model, speed, RAM, HDD,
price) (Laptop) ⋈ PLaptop2(model, speed, RAM, HDD, price) (Laptop) )))) = ф
6. All model of product (PC or Laptop or Printer) in PC, Laptop and Printer relation
must appear in Product relation.
πmodel (Product) – (πmodel (PC) U πmodel (Laptop) U πmodel (Printer)) = ф
