Download presentation

Presentation is loading. Please wait.

Published byLeroy Soulsby Modified over 4 years ago

1
1 Relational Algebra & Calculus Chapter 4, Part A (Relational Algebra) Query Formulation Exercise

2
2 Exercises Given relational schema: Sailors (sid, sname, rating, age) Reservation (sid, bid, date) Boats (bid, bname, color) 1) Find names of sailors who’ve reserved boat #103 2) Find names of sailors who’ve reserved a red boat 3) Find sailors who’ve reserved a red or a green boat 4) Find sailors who’ve reserved a red and a green boat 5) Find the names of sailors who’ve reserved all boats

3
3 1) Find names of sailors who’ve reserved boat #103 Solution 1: Solution 2 : Solution 3 :

4
4 2) Find names of sailors who’ve reserved a red boat Boats (bid, bname, color) Information about boat color only available in Boats; so need an extra join: A more efficient solution -- why more efficient? A query optimizer can find this, given the first solution!

5
5 3) Find sailors who’ve reserved a red or a green boat Can identify all red or green boats, then find sailors who’ve reserved one of these boats: Can also define Tempboats using union! (How?) What happens if is replaced by in this query?

6
6 4) Find sailors who’ve reserved a red and a green boat Previous approach won’t work! Why? Must identify sailors who’ve reserved red boats, sailors who’ve reserved green boats, then find the intersection (note that sid is a key for Sailors):

7
7 4) Find sailors who’ve reserved a red and a green boat Previous approach won’t work! Why? Must identify sailors who’ve reserved red boats, sailors who’ve reserved green boats, then find the intersection (note that sid is a key for Sailors):

8
8 5) Find the names of sailors who’ve reserved all boats Uses division; schemas of the input relations to division (/) must be carefully chosen: To find sailors who’ve reserved all ‘Interlake’ boats:.....

Similar presentations

OK

Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke1 Relational Algebra Chapter 4.

Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke1 Relational Algebra Chapter 4.

© 2018 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google